diff --git a/scripts/processDiagnosticMessages.ts b/scripts/processDiagnosticMessages.ts
index 6a4aaad9f93ee..eccfb821bb220 100644
--- a/scripts/processDiagnosticMessages.ts
+++ b/scripts/processDiagnosticMessages.ts
@@ -3,6 +3,7 @@
 interface DiagnosticDetails {
     category: string;
     code: number;
+    isEarly?: boolean;
 }
 
 interface InputDiagnosticMessageTable {
@@ -63,8 +64,9 @@ function buildInfoFileOutput(messageTable: InputDiagnosticMessageTable, nameMap:
         '        ' + convertPropertyName(nameMap[name]) +
         ': { code: ' + diagnosticDetails.code +
         ', category: DiagnosticCategory.' + diagnosticDetails.category +
-        ', key: "' + name.replace('"', '\\"') +
-        '" },\r\n';
+        ', key: "' + name.replace('"', '\\"') + '"' +
+        (diagnosticDetails.isEarly ? ', isEarly: true' : '') +
+        ' },\r\n';
     }
 
     result += '    };\r\n}';
diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index c9f9d6bf6e3de..accb46504dc5f 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -31,13 +31,14 @@ module ts {
 
         var parent: Node;
         var container: Declaration;
+        var blockScopeContainer: Node;
         var lastContainer: Declaration;
         var symbolCount = 0;
         var Symbol = objectAllocator.getSymbolConstructor();
 
         if (!file.locals) {
             file.locals = {};
-            container = file;
+            container = blockScopeContainer = file;
             bind(file);
             file.symbolCount = symbolCount;
         }
@@ -86,10 +87,11 @@ module ts {
                     }
                     // Report errors every position with duplicate declaration
                     // Report errors on previous encountered declarations
+                    var message = symbol.flags & SymbolFlags.BlockScopedVariable ? Diagnostics.Cannot_redeclare_block_scoped_variable_0 : Diagnostics.Duplicate_identifier_0;
                     forEach(symbol.declarations, (declaration) => {
-                        file.semanticErrors.push(createDiagnosticForNode(declaration.name, Diagnostics.Duplicate_identifier_0, getDisplayName(declaration)));
+                        file.semanticErrors.push(createDiagnosticForNode(declaration.name, message, getDisplayName(declaration)));
                     });
-                    file.semanticErrors.push(createDiagnosticForNode(node.name, Diagnostics.Duplicate_identifier_0, getDisplayName(node)));
+                    file.semanticErrors.push(createDiagnosticForNode(node.name, message, getDisplayName(node)));
 
                     symbol = createSymbol(0, name);
                 }
@@ -167,12 +169,13 @@ module ts {
 
         // All container nodes are kept on a linked list in declaration order. This list is used by the getLocalNameOfContainer function
         // in the type checker to validate that the local name used for a container is unique.
-        function bindChildren(node: Declaration, symbolKind: SymbolFlags) {
+        function bindChildren(node: Declaration, symbolKind: SymbolFlags, isBlockScopeContainer: boolean) {
             if (symbolKind & SymbolFlags.HasLocals) {
                 node.locals = {};
             }
             var saveParent = parent;
             var saveContainer = container;
+            var savedBlockScopeContainer = blockScopeContainer;
             parent = node;
             if (symbolKind & SymbolFlags.IsContainer) {
                 container = node;
@@ -184,12 +187,16 @@ module ts {
                     lastContainer = container;
                 }
             }
+            if (isBlockScopeContainer) {
+                blockScopeContainer = node;
+            }
             forEachChild(node, bind);
             container = saveContainer;
             parent = saveParent;
+            blockScopeContainer = savedBlockScopeContainer;
         }
 
-        function bindDeclaration(node: Declaration, symbolKind: SymbolFlags, symbolExcludes: SymbolFlags) {
+        function bindDeclaration(node: Declaration, symbolKind: SymbolFlags, symbolExcludes: SymbolFlags, isBlockScopeContainer: boolean) {
             switch (container.kind) {
                 case SyntaxKind.ModuleDeclaration:
                     declareModuleMember(node, symbolKind, symbolExcludes);
@@ -225,121 +232,159 @@ module ts {
                     declareSymbol(container.symbol.exports, container.symbol, node, symbolKind, symbolExcludes);
                     break;
             }
-            bindChildren(node, symbolKind);
+            bindChildren(node, symbolKind, isBlockScopeContainer);
         }
 
         function bindConstructorDeclaration(node: ConstructorDeclaration) {
-            bindDeclaration(node, SymbolFlags.Constructor, 0);
+            bindDeclaration(node, SymbolFlags.Constructor, 0, /*isBlockScopeContainer*/ true);
             forEach(node.parameters, p => {
                 if (p.flags & (NodeFlags.Public | NodeFlags.Private | NodeFlags.Protected)) {
-                    bindDeclaration(p, SymbolFlags.Property, SymbolFlags.PropertyExcludes);
+                    bindDeclaration(p, SymbolFlags.Property, SymbolFlags.PropertyExcludes, /*isBlockScopeContainer*/ false);
                 }
             });
         }
 
         function bindModuleDeclaration(node: ModuleDeclaration) {
             if (node.name.kind === SyntaxKind.StringLiteral) {
-                bindDeclaration(node, SymbolFlags.ValueModule, SymbolFlags.ValueModuleExcludes);
+                bindDeclaration(node, SymbolFlags.ValueModule, SymbolFlags.ValueModuleExcludes, /*isBlockScopeContainer*/ true);
             }
             else if (isInstantiated(node)) {
-                bindDeclaration(node, SymbolFlags.ValueModule, SymbolFlags.ValueModuleExcludes);
+                bindDeclaration(node, SymbolFlags.ValueModule, SymbolFlags.ValueModuleExcludes, /*isBlockScopeContainer*/ true);
             }
             else {
-                bindDeclaration(node, SymbolFlags.NamespaceModule, SymbolFlags.NamespaceModuleExcludes);
+                bindDeclaration(node, SymbolFlags.NamespaceModule, SymbolFlags.NamespaceModuleExcludes, /*isBlockScopeContainer*/ true);
             }
         }
 
-        function bindAnonymousDeclaration(node: Node, symbolKind: SymbolFlags, name: string) {
+        function bindAnonymousDeclaration(node: Node, symbolKind: SymbolFlags, name: string, isBlockScopeContainer: boolean) {
             var symbol = createSymbol(symbolKind, name);
             addDeclarationToSymbol(symbol, node, symbolKind);
-            bindChildren(node, symbolKind);
+            bindChildren(node, symbolKind, isBlockScopeContainer);
         }
 
         function bindCatchVariableDeclaration(node: CatchBlock) {
-            var symbol = createSymbol(SymbolFlags.Variable, node.variable.text || "__missing");
-            addDeclarationToSymbol(symbol, node, SymbolFlags.Variable);
+            var symbol = createSymbol(SymbolFlags.FunctionScopedVariable, node.variable.text || "__missing");
+            addDeclarationToSymbol(symbol, node, SymbolFlags.FunctionScopedVariable);
             var saveParent = parent;
-            parent = node;
+            var savedBlockScopeContainer = blockScopeContainer;
+            parent = blockScopeContainer = node;
             forEachChild(node, bind);
             parent = saveParent;
+            blockScopeContainer = savedBlockScopeContainer;
+        }
+
+        function bindBlockScopedVariableDeclaration(node: Declaration) {
+            switch (blockScopeContainer.kind) {
+                case SyntaxKind.ModuleDeclaration:
+                    declareModuleMember(node, SymbolFlags.BlockScopedVariable, SymbolFlags.BlockScopedVariableExcludes);
+                    break;
+                case SyntaxKind.SourceFile:
+                    if (isExternalModule(<SourceFile>container)) {
+                        declareModuleMember(node, SymbolFlags.BlockScopedVariable, SymbolFlags.BlockScopedVariableExcludes);
+                        break;
+                    }
+                default:
+                    if (!blockScopeContainer.locals) {
+                        blockScopeContainer.locals = {};
+                    }
+                    declareSymbol(blockScopeContainer.locals, undefined, node, SymbolFlags.BlockScopedVariable, SymbolFlags.BlockScopedVariableExcludes);
+            }
+
+            bindChildren(node, SymbolFlags.BlockScopedVariable, /*isBlockScopeContainer*/ false);
         }
 
         function bind(node: Node) {
             node.parent = parent;
             switch (node.kind) {
                 case SyntaxKind.TypeParameter:
-                    bindDeclaration(<Declaration>node, SymbolFlags.TypeParameter, SymbolFlags.TypeParameterExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.TypeParameter, SymbolFlags.TypeParameterExcludes, /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.Parameter:
-                    bindDeclaration(<Declaration>node, SymbolFlags.Variable, SymbolFlags.ParameterExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.FunctionScopedVariable, SymbolFlags.ParameterExcludes, /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.VariableDeclaration:
-                    bindDeclaration(<Declaration>node, SymbolFlags.Variable, SymbolFlags.VariableExcludes);
+                    if (node.flags & NodeFlags.BlockScoped) {
+                        bindBlockScopedVariableDeclaration(<Declaration>node);
+                    }
+                    else {
+                        bindDeclaration(<Declaration>node, SymbolFlags.FunctionScopedVariable, SymbolFlags.FunctionScopedVariableExcludes, /*isBlockScopeContainer*/ false);
+                    }
                     break;
                 case SyntaxKind.Property:
                 case SyntaxKind.PropertyAssignment:
-                    bindDeclaration(<Declaration>node, SymbolFlags.Property, SymbolFlags.PropertyExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.Property, SymbolFlags.PropertyExcludes, /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.EnumMember:
-                    bindDeclaration(<Declaration>node, SymbolFlags.EnumMember, SymbolFlags.EnumMemberExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.EnumMember, SymbolFlags.EnumMemberExcludes, /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.CallSignature:
-                    bindDeclaration(<Declaration>node, SymbolFlags.CallSignature, 0);
+                    bindDeclaration(<Declaration>node, SymbolFlags.CallSignature, 0, /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.Method:
-                    bindDeclaration(<Declaration>node, SymbolFlags.Method, SymbolFlags.MethodExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.Method, SymbolFlags.MethodExcludes, /*isBlockScopeContainer*/ true);
                     break;
                 case SyntaxKind.ConstructSignature:
-                    bindDeclaration(<Declaration>node, SymbolFlags.ConstructSignature, 0);
+                    bindDeclaration(<Declaration>node, SymbolFlags.ConstructSignature, 0, /*isBlockScopeContainer*/ true);
                     break;
                 case SyntaxKind.IndexSignature:
-                    bindDeclaration(<Declaration>node, SymbolFlags.IndexSignature, 0);
+                    bindDeclaration(<Declaration>node, SymbolFlags.IndexSignature, 0, /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.FunctionDeclaration:
-                    bindDeclaration(<Declaration>node, SymbolFlags.Function, SymbolFlags.FunctionExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.Function, SymbolFlags.FunctionExcludes, /*isBlockScopeContainer*/ true);
                     break;
                 case SyntaxKind.Constructor:
                     bindConstructorDeclaration(<ConstructorDeclaration>node);
                     break;
                 case SyntaxKind.GetAccessor:
-                    bindDeclaration(<Declaration>node, SymbolFlags.GetAccessor, SymbolFlags.GetAccessorExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.GetAccessor, SymbolFlags.GetAccessorExcludes, /*isBlockScopeContainer*/ true);
                     break;
                 case SyntaxKind.SetAccessor:
-                    bindDeclaration(<Declaration>node, SymbolFlags.SetAccessor, SymbolFlags.SetAccessorExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.SetAccessor, SymbolFlags.SetAccessorExcludes, /*isBlockScopeContainer*/ true);
                     break;
                 case SyntaxKind.TypeLiteral:
-                    bindAnonymousDeclaration(node, SymbolFlags.TypeLiteral, "__type");
+                    bindAnonymousDeclaration(node, SymbolFlags.TypeLiteral, "__type", /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.ObjectLiteral:
-                    bindAnonymousDeclaration(node, SymbolFlags.ObjectLiteral, "__object");
+                    bindAnonymousDeclaration(node, SymbolFlags.ObjectLiteral, "__object", /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.FunctionExpression:
                 case SyntaxKind.ArrowFunction:
-                    bindAnonymousDeclaration(node, SymbolFlags.Function, "__function");
+                    bindAnonymousDeclaration(node, SymbolFlags.Function, "__function", /*isBlockScopeContainer*/ true);
                     break;
                 case SyntaxKind.CatchBlock:
                     bindCatchVariableDeclaration(<CatchBlock>node);
                     break;
                 case SyntaxKind.ClassDeclaration:
-                    bindDeclaration(<Declaration>node, SymbolFlags.Class, SymbolFlags.ClassExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.Class, SymbolFlags.ClassExcludes, /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.InterfaceDeclaration:
-                    bindDeclaration(<Declaration>node, SymbolFlags.Interface, SymbolFlags.InterfaceExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.Interface, SymbolFlags.InterfaceExcludes, /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.EnumDeclaration:
-                    bindDeclaration(<Declaration>node, SymbolFlags.Enum, SymbolFlags.EnumExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.Enum, SymbolFlags.EnumExcludes, /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.ModuleDeclaration:
                     bindModuleDeclaration(<ModuleDeclaration>node);
                     break;
                 case SyntaxKind.ImportDeclaration:
-                    bindDeclaration(<Declaration>node, SymbolFlags.Import, SymbolFlags.ImportExcludes);
+                    bindDeclaration(<Declaration>node, SymbolFlags.Import, SymbolFlags.ImportExcludes, /*isBlockScopeContainer*/ false);
                     break;
                 case SyntaxKind.SourceFile:
                     if (isExternalModule(<SourceFile>node)) {
-                        bindAnonymousDeclaration(node, SymbolFlags.ValueModule, '"' + removeFileExtension((<SourceFile>node).filename) + '"');
+                        bindAnonymousDeclaration(node, SymbolFlags.ValueModule, '"' + removeFileExtension((<SourceFile>node).filename) + '"', /*isBlockScopeContainer*/ true);
                         break;
                     }
+
+                case SyntaxKind.Block:
+                case SyntaxKind.TryBlock:
+                case SyntaxKind.CatchBlock:
+                case SyntaxKind.FinallyBlock:
+                case SyntaxKind.ForStatement:
+                case SyntaxKind.ForInStatement:
+                case SyntaxKind.SwitchStatement:
+                    bindChildren(node, 0 , true);
+                    break;
+
                 default:
                     var saveParent = parent;
                     parent = node;
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 67421879caec2..7a959c0dbfc4a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -108,7 +108,8 @@ module ts {
             isImplementationOfOverload: isImplementationOfOverload,
             getAliasedSymbol: resolveImport,
             isUndefinedSymbol: symbol => symbol === undefinedSymbol,
-            isArgumentsSymbol: symbol => symbol === argumentsSymbol
+            isArgumentsSymbol: symbol => symbol === argumentsSymbol,
+            hasEarlyErrors: hasEarlyErrors
         };
 
         var undefinedSymbol = createSymbol(SymbolFlags.Property | SymbolFlags.Transient, "undefined");
@@ -176,7 +177,8 @@ module ts {
 
         function getExcludedSymbolFlags(flags: SymbolFlags): SymbolFlags {
             var result: SymbolFlags = 0;
-            if (flags & SymbolFlags.Variable) result |= SymbolFlags.VariableExcludes;
+            if (flags & SymbolFlags.BlockScopedVariable) result |= SymbolFlags.BlockScopedVariableExcludes;
+            if (flags & SymbolFlags.FunctionScopedVariable) result |= SymbolFlags.FunctionScopedVariableExcludes;
             if (flags & SymbolFlags.Property) result |= SymbolFlags.PropertyExcludes;
             if (flags & SymbolFlags.EnumMember) result |= SymbolFlags.EnumMemberExcludes;
             if (flags & SymbolFlags.Function) result |= SymbolFlags.FunctionExcludes;
@@ -226,8 +228,13 @@ module ts {
                 recordMergedSymbol(target, source);
             }
             else {
+                var message = target.flags & SymbolFlags.BlockScopedVariable || source.flags & SymbolFlags.BlockScopedVariable
+                     ? Diagnostics.Cannot_redeclare_block_scoped_variable_0 : Diagnostics.Duplicate_identifier_0;
                 forEach(source.declarations, node => {
-                    error(node.name ? node.name : node, Diagnostics.Duplicate_identifier_0, symbolToString(source));
+                    error(node.name ? node.name : node, message, symbolToString(source));
+                });
+                forEach(target.declarations, node => {
+                    error(node.name ? node.name : node, message, symbolToString(source));
                 });
             }
         }
@@ -318,6 +325,25 @@ module ts {
                 if (!s && nameNotFoundMessage) {
                     error(errorLocation, nameNotFoundMessage, nameArg);
                 }
+
+                if (s && s.flags & SymbolFlags.BlockScopedVariable) {
+                    // Block-scoped variables can not be used before their definition
+                    var declaration = forEach(s.declarations, d => d.flags & NodeFlags.BlockScoped ? d : undefined);
+                    Debug.assert(declaration, "Block-scoped variable declaration is undefined");
+                    var declarationSourceFile = getSourceFileOfNode(declaration);
+                    var referenceSourceFile = getSourceFileOfNode(errorLocation);
+                    if (declarationSourceFile === referenceSourceFile) {
+                        if (declaration.pos > errorLocation.pos) {
+                            error(errorLocation, Diagnostics.Block_scoped_variable_0_used_before_its_declaration, identifierToString(declaration.name));
+                        }
+                    }
+                    else if (compilerOptions.out) {
+                        var sourceFiles = program.getSourceFiles();
+                        if (sourceFiles.indexOf(referenceSourceFile) < sourceFiles.indexOf(declarationSourceFile)) {
+                            error(errorLocation, Diagnostics.Block_scoped_variable_0_used_before_its_declaration, identifierToString(declaration.name));
+                        }
+                    }
+                }
                 return s;
             }
 
@@ -5597,7 +5623,7 @@ module ts {
             return true;
         }
 
-        function checkReferenceExpression(n: Node, message: DiagnosticMessage): boolean {
+        function checkReferenceExpression(n: Node, invalidReferenceMessage: DiagnosticMessage, constantVarianleMessage: DiagnosticMessage): boolean {
             function findSymbol(n: Node): Symbol {
                 var symbol = getNodeLinks(n).resolvedSymbol;
                 // Because we got the symbol from the resolvedSymbol property, it might be of kind
@@ -5636,8 +5662,34 @@ module ts {
                 }
             }
 
+            function isConstVariableReference(n: Node): boolean {
+                switch (n.kind) {
+                    case SyntaxKind.Identifier:
+                    case SyntaxKind.PropertyAccess:
+                        var symbol = findSymbol(n);
+                        return symbol && (symbol.flags & SymbolFlags.Variable) !== 0 && (getDeclarationFlagsFromSymbol(symbol) & NodeFlags.Const) !== 0;
+                    case SyntaxKind.IndexedAccess:
+                        var index = (<IndexedAccess>n).index;
+                        var symbol = findSymbol((<IndexedAccess>n).object);
+                        if (symbol && index.kind === SyntaxKind.StringLiteral) {
+                            var name = (<LiteralExpression>index).text;
+                            var prop = getPropertyOfType(getTypeOfSymbol(symbol), name);
+                            return prop && (prop.flags & SymbolFlags.Variable) !== 0 && (getDeclarationFlagsFromSymbol(prop) & NodeFlags.Const) !== 0;
+                        }
+                        return false;
+                    case SyntaxKind.ParenExpression:
+                        return isConstVariableReference((<ParenExpression>n).expression);
+                    default:
+                        return false;
+                }
+            }
+
             if (!isReferenceOrErrorExpression(n)) {
-                error(n, message);
+                error(n, invalidReferenceMessage);
+                return false;
+            }
+            if (isConstVariableReference(n)) {
+                error(n, constantVarianleMessage);
                 return false;
             }
             return true;
@@ -5662,7 +5714,9 @@ module ts {
                     var ok = checkArithmeticOperandType(node.operand, operandType, Diagnostics.An_arithmetic_operand_must_be_of_type_any_number_or_an_enum_type);
                     if (ok) {
                         // run check only if former checks succeeded to avoid reporting cascading errors
-                        checkReferenceExpression(node.operand, Diagnostics.The_operand_of_an_increment_or_decrement_operator_must_be_a_variable_property_or_indexer);
+                        checkReferenceExpression(node.operand,
+                            Diagnostics.The_operand_of_an_increment_or_decrement_operator_must_be_a_variable_property_or_indexer,
+                            Diagnostics.The_operand_of_an_increment_or_decrement_operator_cannot_be_a_constant);
                     }
                     return numberType;
             }
@@ -5674,7 +5728,9 @@ module ts {
             var ok = checkArithmeticOperandType(node.operand, operandType, Diagnostics.An_arithmetic_operand_must_be_of_type_any_number_or_an_enum_type);
             if (ok) {
                 // run check only if former checks succeeded to avoid reporting cascading errors
-                checkReferenceExpression(node.operand, Diagnostics.The_operand_of_an_increment_or_decrement_operator_must_be_a_variable_property_or_indexer);
+                checkReferenceExpression(node.operand,
+                    Diagnostics.The_operand_of_an_increment_or_decrement_operator_must_be_a_variable_property_or_indexer,
+                    Diagnostics.The_operand_of_an_increment_or_decrement_operator_cannot_be_a_constant);
             }
             return numberType;
         }
@@ -5855,7 +5911,7 @@ module ts {
                     // requires VarExpr to be classified as a reference
                     // A compound assignment furthermore requires VarExpr to be classified as a reference (section 4.1) 
                     // and the type of the non - compound operation to be assignable to the type of VarExpr.
-                    var ok = checkReferenceExpression(node.left, Diagnostics.Invalid_left_hand_side_of_assignment_expression);
+                    var ok = checkReferenceExpression(node.left, Diagnostics.Invalid_left_hand_side_of_assignment_expression, Diagnostics.Left_hand_side_of_assignment_expression_cannot_be_a_constant);
                     // Use default messages
                     if (ok) {
                         // to avoid cascading errors check assignability only if 'isReference' check succeeded and no errors were reported
@@ -6829,6 +6885,38 @@ module ts {
             }
         }
 
+        function checkCollisionWithConstDeclarations(node: VariableDeclaration) {
+            // Variable declarations are hoisted to the top of their function scope. They can shadow
+            // block scoped declarations, which bind tighter. this will not be flagged as duplicate definition
+            // by the binder as the declaration scope is different.
+            // A non-initialized declaration is a no-op as the block declaration will resolve before the var
+            // declaration. the problem is if the declaration has an initializer. this will act as a write to the
+            // block declared value. this is fine for let, but not const.
+            //
+            // Only consider declarations with initializers, uninitialized var declarations will not 
+            // step on a const variable.
+            // Do not consider let and const declarations, as duplicate block-scoped declarations 
+            // are handled by the binder.
+            // We are only looking for var declarations that step on const declarations from a 
+            // different scope. e.g.:
+            //      var x = 0;
+            //      {
+            //          const x = 0;
+            //          var x = 0;
+            //      }
+            if (node.initializer && (node.flags & NodeFlags.BlockScoped) === 0) {
+                var symbol = getSymbolOfNode(node);
+                if (symbol.flags & SymbolFlags.FunctionScopedVariable) {
+                    var localDeclarationSymbol = resolveName(node, node.name.text, SymbolFlags.Variable, /*nodeNotFoundErrorMessage*/ undefined, /*nameArg*/ undefined);
+                    if (localDeclarationSymbol && localDeclarationSymbol !== symbol && localDeclarationSymbol.flags & SymbolFlags.BlockScopedVariable) {
+                        if (getDeclarationFlagsFromSymbol(localDeclarationSymbol) & NodeFlags.Const) {
+                            error(node, Diagnostics.Cannot_redeclare_block_scoped_variable_0, symbolToString(localDeclarationSymbol));
+                        }
+                    }
+                }
+            }
+        }
+
         function checkVariableDeclaration(node: VariableDeclaration) {
             checkSourceElement(node.type);
             checkExportsOnMergedDeclarations(node);
@@ -6852,6 +6940,7 @@ module ts {
                         // Use default messages
                         checkTypeAssignableTo(checkAndMarkExpression(node.initializer), type, node, /*chainedMessage*/ undefined, /*terminalMessage*/ undefined);
                     }
+                    checkCollisionWithConstDeclarations(node);
                 }
 
                 checkCollisionWithCapturedSuperVariable(node, node.name);
@@ -6925,7 +7014,7 @@ module ts {
                 }
                 else {
                     // run check only former check succeeded to avoid cascading errors
-                    checkReferenceExpression(node.variable, Diagnostics.Invalid_left_hand_side_in_for_in_statement); 
+                    checkReferenceExpression(node.variable, Diagnostics.Invalid_left_hand_side_in_for_in_statement, Diagnostics.Left_hand_side_of_assignment_expression_cannot_be_a_constant); 
                 }
             }
 
@@ -8227,6 +8316,10 @@ module ts {
             return getDiagnostics().length > 0 || getGlobalDiagnostics().length > 0;
         }
 
+        function hasEarlyErrors(sourceFile?: SourceFile): boolean {
+            return forEach(getDiagnostics(sourceFile), d => d.isEarly);
+        }
+
         function isReferencedImportDeclaration(node: ImportDeclaration): boolean {
             var symbol = getSymbolOfNode(node);
             if (getSymbolLinks(symbol).referenced) {
@@ -8310,6 +8403,7 @@ module ts {
                 getEnumMemberValue: getEnumMemberValue,
                 isTopLevelValueImportedViaEntityName: isTopLevelValueImportedViaEntityName,
                 hasSemanticErrors: hasSemanticErrors,
+                hasEarlyErrors: hasEarlyErrors,
                 isDeclarationVisible: isDeclarationVisible,
                 isImplementationOfOverload: isImplementationOfOverload,
                 writeTypeAtLocation: writeTypeAtLocation,
diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 0e48953eaa7d5..a7993484c647d 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -102,10 +102,10 @@ module ts {
         {
             name: "target",
             shortName: "t",
-            type: { "es3": ScriptTarget.ES3, "es5": ScriptTarget.ES5 },
-            description: Diagnostics.Specify_ECMAScript_target_version_Colon_ES3_default_or_ES5,
+            type: { "es3": ScriptTarget.ES3, "es5": ScriptTarget.ES5 , "es6": ScriptTarget.ES6 },
+            description: Diagnostics.Specify_ECMAScript_target_version_Colon_ES3_default_ES5_or_ES6_experimental,
             paramType: Diagnostics.VERSION,
-            error: Diagnostics.Argument_for_target_option_must_be_es3_or_es5
+            error: Diagnostics.Argument_for_target_option_must_be_es3_es5_or_es6
         },
         {
             name: "version",
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index ee7f4701d19d9..ae2cf05312376 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -232,7 +232,8 @@ module ts {
 
             messageText: text,
             category: message.category,
-            code: message.code
+            code: message.code,
+            isEarly: message.isEarly
         };
     }
 
@@ -251,7 +252,8 @@ module ts {
 
             messageText: text,
             category: message.category,
-            code: message.code
+            code: message.code,
+            isEarly: message.isEarly
         };
     }
 
diff --git a/src/compiler/diagnosticInformationMap.generated.ts b/src/compiler/diagnosticInformationMap.generated.ts
index ac2a79c603d5f..a5dda0b1f4b71 100644
--- a/src/compiler/diagnosticInformationMap.generated.ts
+++ b/src/compiler/diagnosticInformationMap.generated.ts
@@ -114,7 +114,12 @@ module ts {
         Cannot_compile_external_modules_unless_the_module_flag_is_provided: { code: 1148, category: DiagnosticCategory.Error, key: "Cannot compile external modules unless the '--module' flag is provided." },
         Filename_0_differs_from_already_included_filename_1_only_in_casing: { code: 1149, category: DiagnosticCategory.Error, key: "Filename '{0}' differs from already included filename '{1}' only in casing" },
         new_T_cannot_be_used_to_create_an_array_Use_new_Array_T_instead: { code: 1150, category: DiagnosticCategory.Error, key: "'new T[]' cannot be used to create an array. Use 'new Array<T>()' instead." },
-        An_enum_member_cannot_have_a_numeric_name: { code: 1151, category: DiagnosticCategory.Error, key: "An enum member cannot have a numeric name." },
+        var_let_or_const_expected: { code: 1152, category: DiagnosticCategory.Error, key: "'var', 'let' or 'const' expected." },
+        let_declarations_are_only_available_when_targeting_ECMAScript_6_and_higher: { code: 1153, category: DiagnosticCategory.Error, key: "'let' declarations are only available when targeting ECMAScript 6 and higher." },
+        const_declarations_are_only_available_when_targeting_ECMAScript_6_and_higher: { code: 1154, category: DiagnosticCategory.Error, key: "'const' declarations are only available when targeting ECMAScript 6 and higher." },
+        const_declarations_must_be_initialized: { code: 1155, category: DiagnosticCategory.Error, key: "'const' declarations must be initialized" },
+        const_declarations_can_only_be_declared_inside_a_block: { code: 1156, category: DiagnosticCategory.Error, key: "'const' declarations can only be declared inside a block." },
+        let_declarations_can_only_be_declared_inside_a_block: { code: 1157, category: DiagnosticCategory.Error, key: "'let' declarations can only be declared inside a block." },
         Duplicate_identifier_0: { code: 2300, category: DiagnosticCategory.Error, key: "Duplicate identifier '{0}'." },
         Initializer_of_instance_member_variable_0_cannot_reference_identifier_1_declared_in_the_constructor: { code: 2301, category: DiagnosticCategory.Error, key: "Initializer of instance member variable '{0}' cannot reference identifier '{1}' declared in the constructor." },
         Static_members_cannot_reference_class_type_parameters: { code: 2302, category: DiagnosticCategory.Error, key: "Static members cannot reference class type parameters." },
@@ -261,6 +266,11 @@ module ts {
         Property_0_is_protected_and_only_accessible_within_class_1_and_its_subclasses: { code: 2445, category: DiagnosticCategory.Error, key: "Property '{0}' is protected and only accessible within class '{1}' and its subclasses." },
         Property_0_is_protected_and_only_accessible_through_an_instance_of_class_1: { code: 2446, category: DiagnosticCategory.Error, key: "Property '{0}' is protected and only accessible through an instance of class '{1}'." },
         The_0_operator_is_not_allowed_for_boolean_types_Consider_using_1_instead: { code: 2447, category: DiagnosticCategory.Error, key: "The '{0}' operator is not allowed for boolean types. Consider using '{1}' instead." },
+        Block_scoped_variable_0_used_before_its_declaration: { code: 2448, category: DiagnosticCategory.Error, key: "Block-scoped variable '{0}' used before its declaration.", isEarly: true },
+        The_operand_of_an_increment_or_decrement_operator_cannot_be_a_constant: { code: 2449, category: DiagnosticCategory.Error, key: "The operand of an increment or decrement operator cannot be a constant.", isEarly: true },
+        Left_hand_side_of_assignment_expression_cannot_be_a_constant: { code: 2450, category: DiagnosticCategory.Error, key: "Left-hand side of assignment expression cannot be a constant.", isEarly: true },
+        Cannot_redeclare_block_scoped_variable_0: { code: 2451, category: DiagnosticCategory.Error, key: "Cannot redeclare block-scoped variable '{0}'.", isEarly: true },
+        An_enum_member_cannot_have_a_numeric_name: { code: 2452, category: DiagnosticCategory.Error, key: "An enum member cannot have a numeric name." },
         Import_declaration_0_is_using_private_name_1: { code: 4000, category: DiagnosticCategory.Error, key: "Import declaration '{0}' is using private name '{1}'." },
         Type_parameter_0_of_exported_class_has_or_is_using_name_1_from_private_module_2: { code: 4001, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported class has or is using name '{1}' from private module '{2}'." },
         Type_parameter_0_of_exported_class_has_or_is_using_private_name_1: { code: 4002, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported class has or is using private name '{1}'." },
@@ -355,7 +365,7 @@ module ts {
         Watch_input_files: { code: 6005, category: DiagnosticCategory.Message, key: "Watch input files." },
         Redirect_output_structure_to_the_directory: { code: 6006, category: DiagnosticCategory.Message, key: "Redirect output structure to the directory." },
         Do_not_emit_comments_to_output: { code: 6009, category: DiagnosticCategory.Message, key: "Do not emit comments to output." },
-        Specify_ECMAScript_target_version_Colon_ES3_default_or_ES5: { code: 6015, category: DiagnosticCategory.Message, key: "Specify ECMAScript target version: 'ES3' (default), or 'ES5'" },
+        Specify_ECMAScript_target_version_Colon_ES3_default_ES5_or_ES6_experimental: { code: 6015, category: DiagnosticCategory.Message, key: "Specify ECMAScript target version: 'ES3' (default), 'ES5', or 'ES6' (experimental)" },
         Specify_module_code_generation_Colon_commonjs_or_amd: { code: 6016, category: DiagnosticCategory.Message, key: "Specify module code generation: 'commonjs' or 'amd'" },
         Print_this_message: { code: 6017, category: DiagnosticCategory.Message, key: "Print this message." },
         Print_the_compiler_s_version: { code: 6019, category: DiagnosticCategory.Message, key: "Print the compiler's version." },
@@ -377,7 +387,7 @@ module ts {
         Compiler_option_0_expects_an_argument: { code: 6044, category: DiagnosticCategory.Error, key: "Compiler option '{0}' expects an argument." },
         Unterminated_quoted_string_in_response_file_0: { code: 6045, category: DiagnosticCategory.Error, key: "Unterminated quoted string in response file '{0}'." },
         Argument_for_module_option_must_be_commonjs_or_amd: { code: 6046, category: DiagnosticCategory.Error, key: "Argument for '--module' option must be 'commonjs' or 'amd'." },
-        Argument_for_target_option_must_be_es3_or_es5: { code: 6047, category: DiagnosticCategory.Error, key: "Argument for '--target' option must be 'es3' or 'es5'." },
+        Argument_for_target_option_must_be_es3_es5_or_es6: { code: 6047, category: DiagnosticCategory.Error, key: "Argument for '--target' option must be 'es3', 'es5', or 'es6'." },
         Locale_must_be_of_the_form_language_or_language_territory_For_example_0_or_1: { code: 6048, category: DiagnosticCategory.Error, key: "Locale must be of the form <language> or <language>-<territory>. For example '{0}' or '{1}'." },
         Unsupported_locale_0: { code: 6049, category: DiagnosticCategory.Error, key: "Unsupported locale '{0}'." },
         Unable_to_open_file_0: { code: 6050, category: DiagnosticCategory.Error, key: "Unable to open file '{0}'." },
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index d8895d151442a..1336af21aaf80 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -447,9 +447,29 @@
         "category": "Error",
         "code": 1150
     },
-    "An enum member cannot have a numeric name.": {
+    "'var', 'let' or 'const' expected.": {
+        "category": "Error",
+        "code": 1152
+    },
+    "'let' declarations are only available when targeting ECMAScript 6 and higher.": {
+        "category": "Error",
+        "code": 1153
+    },
+    "'const' declarations are only available when targeting ECMAScript 6 and higher.": {
+        "category": "Error",
+        "code": 1154
+    },
+    "'const' declarations must be initialized": {
+        "category": "Error",
+        "code": 1155
+    },
+    "'const' declarations can only be declared inside a block.": {
+        "category": "Error",
+        "code": 1156
+    },
+    "'let' declarations can only be declared inside a block.": {
         "category": "Error",
-        "code":  1151
+        "code": 1157
     },
 
     "Duplicate identifier '{0}'.": {
@@ -1036,6 +1056,30 @@
         "category": "Error",
         "code": 2447
     },
+    "Block-scoped variable '{0}' used before its declaration.": {
+        "category": "Error",
+        "code": 2448,
+        "isEarly": true
+    },
+    "The operand of an increment or decrement operator cannot be a constant.": {
+        "category": "Error",
+        "code": 2449,
+        "isEarly": true
+    },
+    "Left-hand side of assignment expression cannot be a constant.": {
+        "category": "Error",
+        "code": 2450,
+        "isEarly": true
+    },
+    "Cannot redeclare block-scoped variable '{0}'.": {
+        "category": "Error",
+        "code": 2451,
+        "isEarly": true
+    },
+    "An enum member cannot have a numeric name.": {
+        "category": "Error",
+        "code": 2452
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
@@ -1416,7 +1460,7 @@
         "category": "Message",
         "code": 6009
     },
-    "Specify ECMAScript target version: 'ES3' (default), or 'ES5'": {
+    "Specify ECMAScript target version: 'ES3' (default), 'ES5', or 'ES6' (experimental)": {
         "category": "Message",
         "code": 6015
     },
@@ -1504,7 +1548,7 @@
         "category": "Error",
         "code": 6046
     },
-    "Argument for '--target' option must be 'es3' or 'es5'.": {
+    "Argument for '--target' option must be 'es3', 'es5', or 'es6'.": {
         "category": "Error",
         "code": 6047
     },
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index 4dda5c92ca72b..1517584e4c85f 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -1143,7 +1143,15 @@ module ts {
                 write(" ");
                 endPos = emitToken(SyntaxKind.OpenParenToken, endPos);
                 if (node.declarations) {
-                    emitToken(SyntaxKind.VarKeyword, endPos);
+                    if (node.declarations[0] && node.declarations[0].flags & NodeFlags.Let) {
+                        emitToken(SyntaxKind.LetKeyword, endPos);
+                    }
+                    else if (node.declarations[0] && node.declarations[0].flags & NodeFlags.Const) {
+                        emitToken(SyntaxKind.ConstKeyword, endPos);
+                    }
+                    else {
+                        emitToken(SyntaxKind.VarKeyword, endPos);
+                    }
                     write(" ");
                     emitCommaList(node.declarations, /*includeTrailingComma*/ false);
                 }
@@ -1163,7 +1171,12 @@ module ts {
                 write(" ");
                 endPos = emitToken(SyntaxKind.OpenParenToken, endPos);
                 if (node.declaration) {
-                    emitToken(SyntaxKind.VarKeyword, endPos);
+                    if (node.declaration.flags & NodeFlags.Let) {
+                        emitToken(SyntaxKind.LetKeyword, endPos);
+                    }
+                    else {
+                        emitToken(SyntaxKind.VarKeyword, endPos);
+                    }
                     write(" ");
                     emit(node.declaration);
                 }
@@ -1292,7 +1305,17 @@ module ts {
 
             function emitVariableStatement(node: VariableStatement) {
                 emitLeadingComments(node);
-                if (!(node.flags & NodeFlags.Export)) write("var ");
+                if (!(node.flags & NodeFlags.Export)) {
+                    if (node.flags & NodeFlags.Let) {
+                        write("let ");
+                    }
+                    else if (node.flags & NodeFlags.Const) {
+                        write("const ");
+                    }
+                    else {
+                        write("var ");
+                    }
+                }
                 emitCommaList(node.declarations, /*includeTrailingComma*/ false);
                 write(";");
                 emitTrailingComments(node);
@@ -2829,7 +2852,15 @@ module ts {
                 if (hasDeclarationWithEmit) {
                     emitJsDocComments(node);
                     emitDeclarationFlags(node);
-                    write("var ");
+                    if (node.flags & NodeFlags.Let) {
+                        write("let ");
+                    }
+                    else if (node.flags & NodeFlags.Const) {
+                        write("const ");
+                    }
+                    else {
+                        write("var ");
+                    }
                     emitCommaList(node.declarations, emitVariableDeclaration);
                     write(";");
                     writeLine();
@@ -3240,11 +3271,14 @@ module ts {
         }
 
         var hasSemanticErrors = resolver.hasSemanticErrors();
+        var hasEarlyErrors = resolver.hasEarlyErrors(targetSourceFile);
 
         function emitFile(jsFilePath: string, sourceFile?: SourceFile) {
-            emitJavaScript(jsFilePath, sourceFile);
-            if (!hasSemanticErrors && compilerOptions.declaration) {
-                emitDeclarations(jsFilePath, sourceFile);
+            if (!hasEarlyErrors) {
+                emitJavaScript(jsFilePath, sourceFile);
+                if (!hasSemanticErrors && compilerOptions.declaration) {
+                    emitDeclarations(jsFilePath, sourceFile);
+                }
             }
         }
 
@@ -3284,7 +3318,9 @@ module ts {
 
         // Check and update returnCode for syntactic and semantic
         var returnCode: EmitReturnStatus;
-        if (hasEmitterError) {
+        if (hasEarlyErrors) {
+            returnCode = EmitReturnStatus.AllOutputGenerationSkipped;
+        } else if (hasEmitterError) {
             returnCode = EmitReturnStatus.EmitErrorsEncountered;
         } else if (hasSemanticErrors && compilerOptions.declaration) {
             returnCode = EmitReturnStatus.DeclarationGenerationSkipped;
diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index 46717d3df0f0b..15383a0031b2f 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -2696,11 +2696,14 @@ module ts {
         }
 
         // STATEMENTS
+        function parseStatementAllowingLetDeclaration() {
+            return parseStatement(/*allowLetAndConstDeclarations*/ true);
+        }
 
         function parseBlock(ignoreMissingOpenBrace: boolean, checkForStrictMode: boolean): Block {
             var node = <Block>createNode(SyntaxKind.Block);
             if (parseExpected(SyntaxKind.OpenBraceToken) || ignoreMissingOpenBrace) {
-                node.statements = parseList(ParsingContext.BlockStatements,checkForStrictMode, parseStatement);
+                node.statements = parseList(ParsingContext.BlockStatements, checkForStrictMode, parseStatementAllowingLetDeclaration);
                 parseExpected(SyntaxKind.CloseBraceToken);
             }
             else {
@@ -2746,8 +2749,8 @@ module ts {
             parseExpected(SyntaxKind.OpenParenToken);
             node.expression = parseExpression();
             parseExpected(SyntaxKind.CloseParenToken);
-            node.thenStatement = parseStatement();
-            node.elseStatement = parseOptional(SyntaxKind.ElseKeyword) ? parseStatement() : undefined;
+            node.thenStatement = parseStatement(/*allowLetAndConstDeclarations*/ false);
+            node.elseStatement = parseOptional(SyntaxKind.ElseKeyword) ? parseStatement(/*allowLetAndConstDeclarations*/ false) : undefined;
             return finishNode(node);
         }
 
@@ -2757,7 +2760,7 @@ module ts {
 
             var saveInIterationStatement = inIterationStatement;
             inIterationStatement = ControlBlockContext.Nested;
-            node.statement = parseStatement();
+            node.statement = parseStatement(/*allowLetAndConstDeclarations*/ false);
             inIterationStatement = saveInIterationStatement;
 
             parseExpected(SyntaxKind.WhileKeyword);
@@ -2782,7 +2785,7 @@ module ts {
 
             var saveInIterationStatement = inIterationStatement;
             inIterationStatement = ControlBlockContext.Nested;
-            node.statement = parseStatement();
+            node.statement = parseStatement(/*allowLetAndConstDeclarations*/ false);
             inIterationStatement = saveInIterationStatement;
 
             return finishNode(node);
@@ -2794,10 +2797,28 @@ module ts {
             parseExpected(SyntaxKind.OpenParenToken);
             if (token !== SyntaxKind.SemicolonToken) {
                 if (parseOptional(SyntaxKind.VarKeyword)) {
-                    var declarations = parseVariableDeclarationList(0, true);
+                    var declarations = parseVariableDeclarationList(0, /*noIn*/ true);
+                    if (!declarations.length) {
+                        error(Diagnostics.Variable_declaration_list_cannot_be_empty);
+                    }
+                }
+                else if (parseOptional(SyntaxKind.LetKeyword)) {
+                    var declarations = parseVariableDeclarationList(NodeFlags.Let, /*noIn*/ true);
+                    if (!declarations.length) {
+                        error(Diagnostics.Variable_declaration_list_cannot_be_empty);
+                    }
+                    if (languageVersion < ScriptTarget.ES6) {
+                        grammarErrorAtPos(declarations.pos, declarations.end - declarations.pos, Diagnostics.let_declarations_are_only_available_when_targeting_ECMAScript_6_and_higher);
+                    }
+                }
+                else if (parseOptional(SyntaxKind.ConstKeyword)) {
+                    var declarations = parseVariableDeclarationList(NodeFlags.Const, /*noIn*/ true);
                     if (!declarations.length) {
                         error(Diagnostics.Variable_declaration_list_cannot_be_empty);
                     }
+                    if (languageVersion < ScriptTarget.ES6) {
+                        grammarErrorAtPos(declarations.pos, declarations.end - declarations.pos, Diagnostics.const_declarations_are_only_available_when_targeting_ECMAScript_6_and_higher);
+                    }
                 }
                 else {
                     var varOrInit = parseExpression(true);
@@ -2837,7 +2858,7 @@ module ts {
 
             var saveInIterationStatement = inIterationStatement;
             inIterationStatement = ControlBlockContext.Nested;
-            forOrForInStatement.statement = parseStatement();
+            forOrForInStatement.statement = parseStatement(/*allowLetAndConstDeclarations*/ false);
             inIterationStatement = saveInIterationStatement;
 
             return finishNode(forOrForInStatement);
@@ -2948,7 +2969,7 @@ module ts {
             parseExpected(SyntaxKind.OpenParenToken);
             node.expression = parseExpression();
             parseExpected(SyntaxKind.CloseParenToken);
-            node.statement = parseStatement();
+            node.statement = parseStatement(/*allowLetAndConstDeclarations*/ false);
             node = finishNode(node);
             if (isInStrictMode) {
                 // Strict mode code may not include a WithStatement. The occurrence of a WithStatement in such 
@@ -2963,7 +2984,7 @@ module ts {
             parseExpected(SyntaxKind.CaseKeyword);
             node.expression = parseExpression();
             parseExpected(SyntaxKind.ColonToken);
-            node.statements = parseList(ParsingContext.SwitchClauseStatements, /*checkForStrictMode*/ false, parseStatement);
+            node.statements = parseList(ParsingContext.SwitchClauseStatements, /*checkForStrictMode*/ false, parseStatementAllowingLetDeclaration);
             return finishNode(node);
         }
 
@@ -2971,7 +2992,7 @@ module ts {
             var node = <CaseOrDefaultClause>createNode(SyntaxKind.DefaultClause);
             parseExpected(SyntaxKind.DefaultKeyword);
             parseExpected(SyntaxKind.ColonToken);
-            node.statements = parseList(ParsingContext.SwitchClauseStatements, /*checkForStrictMode*/ false, parseStatement);
+            node.statements = parseList(ParsingContext.SwitchClauseStatements, /*checkForStrictMode*/ false, parseStatementAllowingLetDeclaration);
             return finishNode(node);
         }
 
@@ -3078,9 +3099,9 @@ module ts {
             return token === SyntaxKind.WhileKeyword || token === SyntaxKind.DoKeyword || token === SyntaxKind.ForKeyword;
         }
 
-        function parseStatementWithLabelSet(): Statement {
+        function parseStatementWithLabelSet(allowLetAndConstDeclarations: boolean): Statement {
             labelledStatementInfo.pushCurrentLabelSet(isIterationStatementStart());
-            var statement = parseStatement();
+            var statement = parseStatement(allowLetAndConstDeclarations);
             labelledStatementInfo.pop();
             return statement;
         }
@@ -3089,7 +3110,7 @@ module ts {
             return isIdentifier() && lookAhead(() => nextToken() === SyntaxKind.ColonToken);
         }
 
-        function parseLabelledStatement(): LabeledStatement {
+        function parseLabeledStatement(allowLetAndConstDeclarations: boolean): LabeledStatement {
             var node = <LabeledStatement>createNode(SyntaxKind.LabeledStatement);
             node.label = parseIdentifier();
             parseExpected(SyntaxKind.ColonToken);
@@ -3101,7 +3122,7 @@ module ts {
 
             // We only want to call parseStatementWithLabelSet when the label set is complete
             // Therefore, keep parsing labels until we know we're done.
-            node.statement = isLabel() ? parseLabelledStatement() : parseStatementWithLabelSet();
+            node.statement = isLabel() ? parseLabeledStatement(allowLetAndConstDeclarations) : parseStatementWithLabelSet(allowLetAndConstDeclarations);
             return finishNode(node);
         }
 
@@ -3124,6 +3145,8 @@ module ts {
                     return !inErrorRecovery;
                 case SyntaxKind.OpenBraceToken:
                 case SyntaxKind.VarKeyword:
+                case SyntaxKind.LetKeyword:
+                case SyntaxKind.ConstKeyword:
                 case SyntaxKind.FunctionKeyword:
                 case SyntaxKind.IfKeyword:
                 case SyntaxKind.DoKeyword:
@@ -3165,12 +3188,14 @@ module ts {
             }
         }
 
-        function parseStatement(): Statement {
+        function parseStatement(allowLetAndConstDeclarations: boolean): Statement {
             switch (token) {
                 case SyntaxKind.OpenBraceToken:
                     return parseBlock(/* ignoreMissingOpenBrace */ false, /*checkForStrictMode*/ false);
                 case SyntaxKind.VarKeyword:
-                    return parseVariableStatement();
+                case SyntaxKind.LetKeyword:
+                case SyntaxKind.ConstKeyword:
+                    return parseVariableStatement(allowLetAndConstDeclarations);
                 case SyntaxKind.FunctionKeyword:
                     return parseFunctionDeclaration();
                 case SyntaxKind.SemicolonToken:
@@ -3204,16 +3229,12 @@ module ts {
                     return parseDebuggerStatement();
                 default:
                     if (isLabel()) {
-                        return parseLabelledStatement();
+                        return parseLabeledStatement(allowLetAndConstDeclarations);
                     }
                     return parseExpressionStatement();
             }
         }
 
-        function parseStatementOrFunction(): Statement {
-            return token === SyntaxKind.FunctionKeyword ? parseFunctionDeclaration() : parseStatement();
-        }
-
         function parseAndCheckFunctionBody(isConstructor: boolean): Block {
             var initialPosition = scanner.getTokenPos();
             var errorCountBeforeBody = file.syntacticErrors.length;
@@ -3249,6 +3270,9 @@ module ts {
             if (inAmbientContext && node.initializer && errorCountBeforeVariableDeclaration === file.syntacticErrors.length) {
                 grammarErrorAtPos(initializerStart, initializerFirstTokenLength, Diagnostics.Initializers_are_not_allowed_in_ambient_contexts);
             }
+            if (!inAmbientContext && !node.initializer && flags & NodeFlags.Const) {
+                grammarErrorOnNode(node, Diagnostics.const_declarations_must_be_initialized);
+            }
             if (isInStrictMode && isEvalOrArgumentsIdentifier(node.name)) {
                 // It is a SyntaxError if a VariableDeclaration or VariableDeclarationNoIn occurs within strict code 
                 // and its Identifier is eval or arguments 
@@ -3262,17 +3286,42 @@ module ts {
                 () => parseVariableDeclaration(flags, noIn), /*allowTrailingComma*/ false);
         }
 
-        function parseVariableStatement(pos?: number, flags?: NodeFlags): VariableStatement {
+        function parseVariableStatement(allowLetAndConstDeclarations: boolean, pos?: number, flags?: NodeFlags): VariableStatement {
             var node = <VariableStatement>createNode(SyntaxKind.VariableStatement, pos);
             if (flags) node.flags = flags;
             var errorCountBeforeVarStatement = file.syntacticErrors.length;
-            parseExpected(SyntaxKind.VarKeyword);
-            node.declarations = parseVariableDeclarationList(flags, /*noIn*/false);
+            if (token === SyntaxKind.LetKeyword) {
+                node.flags |= NodeFlags.Let;
+            }
+            else if (token === SyntaxKind.ConstKeyword) {
+                node.flags |= NodeFlags.Const;
+            }
+            else if (token !== SyntaxKind.VarKeyword) {
+                error(Diagnostics.var_let_or_const_expected);
+            }
+            nextToken();
+            node.declarations = parseVariableDeclarationList(node.flags, /*noIn*/false);
             parseSemicolon();
             finishNode(node);
             if (!node.declarations.length && file.syntacticErrors.length === errorCountBeforeVarStatement) {
                 grammarErrorOnNode(node, Diagnostics.Variable_declaration_list_cannot_be_empty);
             }
+            if (languageVersion < ScriptTarget.ES6) {
+                if (node.flags & NodeFlags.Let) {
+                    grammarErrorOnNode(node, Diagnostics.let_declarations_are_only_available_when_targeting_ECMAScript_6_and_higher);
+                }
+                else if (node.flags & NodeFlags.Const) {
+                    grammarErrorOnNode(node, Diagnostics.const_declarations_are_only_available_when_targeting_ECMAScript_6_and_higher);
+                }
+            }
+            else if (!allowLetAndConstDeclarations) {
+                if (node.flags & NodeFlags.Let) {
+                    grammarErrorOnNode(node, Diagnostics.let_declarations_can_only_be_declared_inside_a_block);
+                }
+                else if (node.flags & NodeFlags.Const) {
+                    grammarErrorOnNode(node, Diagnostics.const_declarations_can_only_be_declared_inside_a_block);
+                }
+            }
             return node;
         }
 
@@ -3851,6 +3900,8 @@ module ts {
         function isDeclaration(): boolean {
             switch (token) {
                 case SyntaxKind.VarKeyword:
+                case SyntaxKind.LetKeyword:
+                case SyntaxKind.ConstKeyword:
                 case SyntaxKind.FunctionKeyword:
                     return true;
                 case SyntaxKind.ClassKeyword:
@@ -3901,7 +3952,9 @@ module ts {
             var result: Declaration;
             switch (token) {
                 case SyntaxKind.VarKeyword:
-                    result = parseVariableStatement(pos, flags);
+                case SyntaxKind.LetKeyword:
+                case SyntaxKind.ConstKeyword:
+                    result = parseVariableStatement(/*allowLetAndConstDeclarations*/ true, pos, flags);
                     break;
                 case SyntaxKind.FunctionKeyword:
                     result = parseFunctionDeclaration(pos, flags);
@@ -3949,7 +4002,7 @@ module ts {
             var statementStart = scanner.getTokenPos();
             var statementFirstTokenLength = scanner.getTextPos() - statementStart;
             var errorCountBeforeStatement = file.syntacticErrors.length;
-            var statement = parseStatement();
+            var statement = parseStatement(/*allowLetAndConstDeclarations*/ true);
 
             if (inAmbientContext && file.syntacticErrors.length === errorCountBeforeStatement) {
                 grammarErrorAtPos(statementStart, statementFirstTokenLength, Diagnostics.Statements_are_not_allowed_in_ambient_contexts);
diff --git a/src/compiler/tsc.ts b/src/compiler/tsc.ts
index 52dac9695de17..15f231bc74ea9 100644
--- a/src/compiler/tsc.ts
+++ b/src/compiler/tsc.ts
@@ -361,13 +361,18 @@ module ts {
         else {
             var checker = program.getTypeChecker(/*fullTypeCheckMode*/ true);
             var checkStart = new Date().getTime();
-            var semanticErrors = checker.getDiagnostics();
-            var emitStart = new Date().getTime();
-            var emitOutput = checker.emitFiles();
-            var emitErrors = emitOutput.errors;
-            exitStatus = emitOutput.emitResultStatus;
-            var reportStart = new Date().getTime();
-            errors = concatenate(semanticErrors, emitErrors);
+            errors = checker.getDiagnostics();
+            if (!checker.hasEarlyErrors()) {
+                var emitStart = new Date().getTime();
+                var emitOutput = checker.emitFiles();
+                var emitErrors = emitOutput.errors;
+                exitStatus = emitOutput.emitResultStatus;
+                var reportStart = new Date().getTime();
+                errors = concatenate(errors, emitErrors);
+            }
+            else {
+                exitStatus = EmitReturnStatus.AllOutputGenerationSkipped;
+            }
         }
 
         reportDiagnostics(errors);
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 48c74d8f2af3e..aa2ca3b4ba83a 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -247,9 +247,12 @@ module ts {
         MultiLine        = 0x00000100,  // Multi-line array or object literal
         Synthetic        = 0x00000200,  // Synthetic node (for full fidelity)
         DeclarationFile  = 0x00000400,  // Node is a .d.ts file
+        Let              = 0x00000800,  // Variable declaration
+        Const            = 0x00001000,  // Variable declaration
 
         Modifier = Export | Ambient | Public | Private | Protected | Static,
-        AccessibilityModifier = Public | Private | Protected
+        AccessibilityModifier = Public | Private | Protected,
+        BlockScoped = Let | Const
     }
 
     export interface Node extends TextRange {
@@ -663,6 +666,7 @@ module ts {
         isImplementationOfOverload(node: FunctionDeclaration): boolean;
         isUndefinedSymbol(symbol: Symbol): boolean;
         isArgumentsSymbol(symbol: Symbol): boolean;
+        hasEarlyErrors(sourceFile?: SourceFile): boolean;
 
         // Returns the constant value of this enum member, or 'undefined' if the enum member has a 
         // computed value.
@@ -758,51 +762,62 @@ module ts {
         // Returns the constant value this property access resolves to, or 'undefined' if it does 
         // resolve to a constant.
         getConstantValue(node: PropertyAccess): number;
+        hasEarlyErrors(sourceFile?: SourceFile): boolean;
     }
 
     export enum SymbolFlags {
-        Variable           = 0x00000001,  // Variable or parameter
-        Property           = 0x00000002,  // Property or enum member
-        EnumMember         = 0x00000004,  // Enum member
-        Function           = 0x00000008,  // Function
-        Class              = 0x00000010,  // Class
-        Interface          = 0x00000020,  // Interface
-        Enum               = 0x00000040,  // Enum
-        ValueModule        = 0x00000080,  // Instantiated module
-        NamespaceModule    = 0x00000100,  // Uninstantiated module
-        TypeLiteral        = 0x00000200,  // Type Literal
-        ObjectLiteral      = 0x00000400,  // Object Literal
-        Method             = 0x00000800,  // Method
-        Constructor        = 0x00001000,  // Constructor
-        GetAccessor        = 0x00002000,  // Get accessor
-        SetAccessor        = 0x00004000,  // Set accessor
-        CallSignature      = 0x00008000,  // Call signature
-        ConstructSignature = 0x00010000,  // Construct signature
-        IndexSignature     = 0x00020000,  // Index signature
-        TypeParameter      = 0x00040000,  // Type parameter
+        FunctionScopedVariable = 0x00000001, // Variable (var) or parameter
+        Property               = 0x00000002,  // Property or enum member
+        EnumMember             = 0x00000004,  // Enum member
+        Function               = 0x00000008,  // Function
+        Class                  = 0x00000010,  // Class
+        Interface              = 0x00000020,  // Interface
+        Enum                   = 0x00000040,  // Enum
+        ValueModule            = 0x00000080,  // Instantiated module
+        NamespaceModule        = 0x00000100,  // Uninstantiated module
+        TypeLiteral            = 0x00000200,  // Type Literal
+        ObjectLiteral          = 0x00000400,  // Object Literal
+        Method                 = 0x00000800,  // Method
+        Constructor            = 0x00001000,  // Constructor
+        GetAccessor            = 0x00002000,  // Get accessor
+        SetAccessor            = 0x00004000,  // Set accessor
+        CallSignature          = 0x00008000,  // Call signature
+        ConstructSignature     = 0x00010000,  // Construct signature
+        IndexSignature         = 0x00020000,  // Index signature
+        TypeParameter          = 0x00040000,  // Type parameter
 
         // Export markers (see comment in declareModuleMember in binder)
-        ExportValue        = 0x00080000,  // Exported value marker
-        ExportType         = 0x00100000,  // Exported type marker
-        ExportNamespace    = 0x00200000,  // Exported namespace marker
+        ExportValue            = 0x00080000,  // Exported value marker
+        ExportType             = 0x00100000,  // Exported type marker
+        ExportNamespace        = 0x00200000,  // Exported namespace marker
 
-        Import             = 0x00400000,  // Import
-        Instantiated       = 0x00800000,  // Instantiated symbol
-        Merged             = 0x01000000,  // Merged symbol (created during program binding)
-        Transient          = 0x02000000,  // Transient symbol (created during type check)
-        Prototype          = 0x04000000,  // Prototype property (no source representation)
-        UnionProperty      = 0x08000000,  // Property in union type
+        Import                 = 0x00400000,  // Import
+        Instantiated           = 0x00800000,  // Instantiated symbol
+        Merged                 = 0x01000000,  // Merged symbol (created during program binding)
+        Transient              = 0x02000000,  // Transient symbol (created during type check)
+        Prototype              = 0x04000000,  // Prototype property (no source representation)
+        UnionProperty          = 0x08000000,  // Property in union type
 
+        BlockScopedVariable    = 0x10000000,  // A block-scoped variable (let ot const)
+
+        Variable  = FunctionScopedVariable | BlockScopedVariable,
         Value     = Variable | Property | EnumMember | Function | Class | Enum | ValueModule | Method | GetAccessor | SetAccessor,
-
         Type      = Class | Interface | Enum | TypeLiteral | ObjectLiteral | TypeParameter,
         Namespace = ValueModule | NamespaceModule,
         Module    = ValueModule | NamespaceModule,
         Accessor  = GetAccessor | SetAccessor,
         Signature = CallSignature | ConstructSignature | IndexSignature,
 
+
+        // Variables can be redeclared, but can not redeclare a block-scoped declaration with the 
+        // same name, or any other value that is not a variable, e.g. ValueModule or Class
+        FunctionScopedVariableExcludes = Value & ~FunctionScopedVariable,   
+
+        // Block-scoped declarations are not allowed to be re-declared
+        // they can not merge with anything in the value space
+        BlockScopedVariableExcludes    = Value,
+
         ParameterExcludes       = Value,
-        VariableExcludes        = Value & ~Variable,
         PropertyExcludes        = Value,
         EnumMemberExcludes      = Value,
         FunctionExcludes        = Value & ~(Function | ValueModule),
@@ -816,8 +831,9 @@ module ts {
         SetAccessorExcludes     = Value & ~GetAccessor,
         TypeParameterExcludes   = Type & ~TypeParameter,
 
+
         // Imports collide with all other imports with the same name.
-        ImportExcludes          = Import,
+        ImportExcludes                 = Import,
 
         ModuleMember = Variable | Function | Class | Interface | Enum | Module | Import,
 
@@ -1024,6 +1040,7 @@ module ts {
         key: string;
         category: DiagnosticCategory;
         code: number;
+        isEarly?: boolean;
     }
 
     // A linked list of formatted diagnostic messages to be used as part of a multiline message.
@@ -1044,6 +1061,7 @@ module ts {
         messageText: string;
         category: DiagnosticCategory;
         code: number;
+        isEarly?: boolean;
     }
 
     export enum DiagnosticCategory {
@@ -1096,6 +1114,8 @@ module ts {
     export enum ScriptTarget {
         ES3,
         ES5,
+        ES6,
+        Latest = ES6,
     }
 
     export interface ParsedCommandLine {
diff --git a/src/harness/fourslash.ts b/src/harness/fourslash.ts
index aede75d51da01..33f435ce76b2b 100644
--- a/src/harness/fourslash.ts
+++ b/src/harness/fourslash.ts
@@ -2220,7 +2220,7 @@ module FourSlash {
         var host = Harness.Compiler.createCompilerHost([{ unitName: Harness.Compiler.fourslashFilename, content: undefined },
             { unitName: fileName, content: content }],
             (fn, contents) => result = contents,
-            ts.ScriptTarget.ES5,
+            ts.ScriptTarget.Latest,
             sys.useCaseSensitiveFileNames);
         var program = ts.createProgram([Harness.Compiler.fourslashFilename, fileName], { out: "fourslashTestOutput.js" }, host);
         var checker = ts.createTypeChecker(program, /*fullTypeCheckMode*/ true);
diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index 2f7bf780b4187..60c5da5a1a68a 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -540,7 +540,7 @@ module Harness {
         }
 
         export var defaultLibFileName = 'lib.d.ts';
-        export var defaultLibSourceFile = ts.createSourceFile(defaultLibFileName, IO.readFile(libFolder + 'lib.core.d.ts'), /*languageVersion*/ ts.ScriptTarget.ES5, /*version:*/ "0");
+        export var defaultLibSourceFile = ts.createSourceFile(defaultLibFileName, IO.readFile(libFolder + 'lib.core.d.ts'), /*languageVersion*/ ts.ScriptTarget.Latest, /*version:*/ "0");
 
         // Cache these between executions so we don't have to re-parse them for every test
         export var fourslashFilename = 'fourslash.ts';
@@ -693,6 +693,8 @@ module Harness {
                                     options.target = ts.ScriptTarget.ES3;
                                 } else if (setting.value.toLowerCase() === 'es5') {
                                     options.target = ts.ScriptTarget.ES5;
+                                } else if (setting.value.toLowerCase() === 'es6') {
+                                    options.target = ts.ScriptTarget.ES6;
                                 } else {
                                     throw new Error('Unknown compile target ' + setting.value);
                                 }
@@ -799,9 +801,11 @@ module Harness {
                 var checker = program.getTypeChecker(/*fullTypeCheckMode*/ true);
                 checker.checkProgram();
 
+                var hasEarlyErrors = checker.hasEarlyErrors();
+
                 // only emit if there weren't parse errors
                 var emitResult: ts.EmitResult;
-                if (!hadParseErrors) {
+                if (!hadParseErrors && !hasEarlyErrors) {
                     emitResult = checker.emitFiles();
                 }
 
diff --git a/src/harness/harnessLanguageService.ts b/src/harness/harnessLanguageService.ts
index 647d0729cbb5f..6307c4d1e78ff 100644
--- a/src/harness/harnessLanguageService.ts
+++ b/src/harness/harnessLanguageService.ts
@@ -260,7 +260,7 @@ module Harness.LanguageService {
 
         /** Parse file given its source text */
         public parseSourceText(fileName: string, sourceText: TypeScript.IScriptSnapshot): TypeScript.SourceUnitSyntax {
-            return TypeScript.Parser.parse(fileName, TypeScript.SimpleText.fromScriptSnapshot(sourceText), ts.ScriptTarget.ES5, TypeScript.isDTSFile(fileName)).sourceUnit();
+            return TypeScript.Parser.parse(fileName, TypeScript.SimpleText.fromScriptSnapshot(sourceText), ts.ScriptTarget.Latest, TypeScript.isDTSFile(fileName)).sourceUnit();
         }
 
         /** Parse a file on disk given its fileName */
diff --git a/src/services/compiler/precompile.ts b/src/services/compiler/precompile.ts
index 3ff23d85bea1c..08a919a65b58a 100644
--- a/src/services/compiler/precompile.ts
+++ b/src/services/compiler/precompile.ts
@@ -184,7 +184,7 @@ module TypeScript {
 
     export function preProcessFile(fileName: string, sourceText: IScriptSnapshot, readImportFiles = true): IPreProcessedFileInfo {
         var text = SimpleText.fromScriptSnapshot(sourceText);
-        var scanner = Scanner.createScanner(ts.ScriptTarget.ES5, text, reportDiagnostic);
+        var scanner = Scanner.createScanner(ts.ScriptTarget.Latest, text, reportDiagnostic);
 
         var firstToken = scanner.scan(/*allowRegularExpression:*/ false);
 
diff --git a/src/services/navigationBar.ts b/src/services/navigationBar.ts
index 9f16fa57741d9..6918097412035 100644
--- a/src/services/navigationBar.ts
+++ b/src/services/navigationBar.ts
@@ -233,7 +233,12 @@ module ts.NavigationBar {
                     return createItem(node, getTextOfNode((<FunctionDeclaration>node).name), ts.ScriptElementKind.functionElement);
 
                 case SyntaxKind.VariableDeclaration:
-                    return createItem(node, getTextOfNode((<VariableDeclaration>node).name), ts.ScriptElementKind.variableElement);
+                    if (node.flags & NodeFlags.Const) {
+                        return createItem(node, getTextOfNode((<VariableDeclaration>node).name), ts.ScriptElementKind.constantElement);
+                    }
+                    else {
+                        return createItem(node, getTextOfNode((<VariableDeclaration>node).name), ts.ScriptElementKind.variableElement);
+                    }
                 
                 case SyntaxKind.Constructor:
                     return createItem(node, "constructor", ts.ScriptElementKind.constructorImplementationElement);
diff --git a/src/services/services.ts b/src/services/services.ts
index 75afa46248ce7..d853d06d68e8a 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -77,7 +77,7 @@ module ts {
         update(scriptSnapshot: TypeScript.IScriptSnapshot, version: string, isOpen: boolean, textChangeRange: TypeScript.TextChangeRange): SourceFile;
     }
 
-    var scanner: Scanner = createScanner(ScriptTarget.ES5, /*skipTrivia*/ true);
+    var scanner: Scanner = createScanner(ScriptTarget.Latest, /*skipTrivia*/ true);
 
     var emptyArray: any[] = [];
 
@@ -1235,7 +1235,9 @@ module ts {
 
         static label = "label";
 
-        static alias = "alias"
+        static alias = "alias";
+
+        static constantElement = "constant";
     }
 
     export class ScriptElementKindModifier {
@@ -1486,9 +1488,9 @@ module ts {
     }
 
     export function getDefaultCompilerOptions(): CompilerOptions {
-        // Set "ES5" target by default for language service
+        // Set "ScriptTarget.Latest" target by default for language service
         return {
-            target: ScriptTarget.ES5,
+            target: ScriptTarget.Latest,
             module: ModuleKind.None,
         };
     }
@@ -2733,6 +2735,9 @@ module ts {
                 if (isFirstDeclarationOfSymbolParameter(symbol)) {
                     return ScriptElementKind.parameterElement;
                 }
+                else if(symbol.valueDeclaration && symbol.valueDeclaration.flags & NodeFlags.Const) {
+                    return ScriptElementKind.constantElement;
+                }
                 return isLocalVariableOrFunction(symbol) ? ScriptElementKind.localVariableElement : ScriptElementKind.variableElement;
             }
             if (flags & SymbolFlags.Function) return isLocalVariableOrFunction(symbol) ? ScriptElementKind.localFunctionElement : ScriptElementKind.functionElement;
@@ -2778,7 +2783,7 @@ module ts {
                 case SyntaxKind.ClassDeclaration: return ScriptElementKind.classElement;
                 case SyntaxKind.InterfaceDeclaration: return ScriptElementKind.interfaceElement;
                 case SyntaxKind.EnumDeclaration: return ScriptElementKind.enumElement;
-                case SyntaxKind.VariableDeclaration: return ScriptElementKind.variableElement;
+                case SyntaxKind.VariableDeclaration: return node.flags & NodeFlags.Const ? ScriptElementKind.constantElement: ScriptElementKind.variableElement;
                 case SyntaxKind.FunctionDeclaration: return ScriptElementKind.functionElement;
                 case SyntaxKind.GetAccessor: return ScriptElementKind.memberGetAccessorElement;
                 case SyntaxKind.SetAccessor: return ScriptElementKind.memberSetAccessorElement;
@@ -2867,6 +2872,7 @@ module ts {
                             switch (symbolKind) {
                                 case ScriptElementKind.memberVariableElement:
                                 case ScriptElementKind.variableElement:
+                                case ScriptElementKind.constantElement:
                                 case ScriptElementKind.parameterElement:
                                 case ScriptElementKind.localVariableElement:
                                     // If it is call or construct signature of lambda's write type name
@@ -3891,8 +3897,8 @@ module ts {
                     // before and after it have to be a non-identifier char).
                     var endPosition = position + symbolNameLength;
 
-                    if ((position === 0 || !isIdentifierPart(text.charCodeAt(position - 1), ScriptTarget.ES5)) &&
-                        (endPosition === sourceLength || !isIdentifierPart(text.charCodeAt(endPosition), ScriptTarget.ES5))) {
+                    if ((position === 0 || !isIdentifierPart(text.charCodeAt(position - 1), ScriptTarget.Latest)) &&
+                        (endPosition === sourceLength || !isIdentifierPart(text.charCodeAt(endPosition), ScriptTarget.Latest))) {
                         // Found a real match.  Keep searching.  
                         positions.push(position);
                     }
@@ -5333,7 +5339,7 @@ module ts {
 
     /// Classifier
     export function createClassifier(host: Logger): Classifier {
-        var scanner = createScanner(ScriptTarget.ES5, /*skipTrivia*/ false);
+        var scanner = createScanner(ScriptTarget.Latest, /*skipTrivia*/ false);
 
         /// We do not have a full parser support to know when we should parse a regex or not
         /// If we consider every slash token to be a regex, we could be missing cases like "1/2/3", where
diff --git a/src/services/shims.ts b/src/services/shims.ts
index fdea0202323fb..a6bf421b09566 100644
--- a/src/services/shims.ts
+++ b/src/services/shims.ts
@@ -174,6 +174,7 @@ module ts {
     export enum LanguageVersion {
         EcmaScript3 = 0,
         EcmaScript5 = 1,
+        EcmaScript6 = 2,
     }
 
     export enum ModuleGenTarget {
@@ -213,6 +214,7 @@ module ts {
         switch (languageVersion) {
             case LanguageVersion.EcmaScript3: return ScriptTarget.ES3
             case LanguageVersion.EcmaScript5: return ScriptTarget.ES5;
+            case LanguageVersion.EcmaScript6: return ScriptTarget.ES6;
             default: throw Error("unsupported LanguageVersion value: " + languageVersion);
         }
     }
@@ -234,6 +236,7 @@ module ts {
         switch (scriptTarget) {
             case ScriptTarget.ES3: return LanguageVersion.EcmaScript3;
             case ScriptTarget.ES5: return LanguageVersion.EcmaScript5;
+            case ScriptTarget.ES6: return LanguageVersion.EcmaScript6;
             default: throw Error("unsupported ScriptTarget value: " + scriptTarget);
         }
     }
diff --git a/src/services/syntax/scanner.ts b/src/services/syntax/scanner.ts
index 45cc151e2d5ba..29ced029f1cca 100644
--- a/src/services/syntax/scanner.ts
+++ b/src/services/syntax/scanner.ts
@@ -186,7 +186,7 @@ module TypeScript.Scanner {
     var lastTokenInfo = { leadingTriviaWidth: -1, width: -1 };
     var lastTokenInfoTokenID: number = -1;
 
-    var triviaScanner = createScannerInternal(ts.ScriptTarget.ES5, SimpleText.fromString(""), () => { });
+    var triviaScanner = createScannerInternal(ts.ScriptTarget.Latest, SimpleText.fromString(""), () => { });
 
     interface IScannerToken extends ISyntaxToken {
     }
diff --git a/src/services/syntax/unicode.ts b/src/services/syntax/unicode.ts
index df2f88b74c576..b1e94090de743 100644
--- a/src/services/syntax/unicode.ts
+++ b/src/services/syntax/unicode.ts
@@ -84,7 +84,7 @@ module TypeScript {
             if (languageVersion === ts.ScriptTarget.ES3) {
                 return Unicode.lookupInUnicodeMap(code, Unicode.unicodeES3IdentifierStart);
             }
-            else if (languageVersion === ts.ScriptTarget.ES5) {
+            else if (languageVersion >= ts.ScriptTarget.ES5) {
                 return Unicode.lookupInUnicodeMap(code, Unicode.unicodeES5IdentifierStart);
             }
             else {
@@ -96,7 +96,7 @@ module TypeScript {
             if (languageVersion === ts.ScriptTarget.ES3) {
                 return Unicode.lookupInUnicodeMap(code, Unicode.unicodeES3IdentifierPart);
             }
-            else if (languageVersion === ts.ScriptTarget.ES5) {
+            else if (languageVersion >= ts.ScriptTarget.ES5) {
                 return Unicode.lookupInUnicodeMap(code, Unicode.unicodeES5IdentifierPart);
             }
             else {
diff --git a/tests/baselines/reference/constDeclarationShadowedByVarDeclaration.errors.txt b/tests/baselines/reference/constDeclarationShadowedByVarDeclaration.errors.txt
new file mode 100644
index 0000000000000..629cf7f75af7e
--- /dev/null
+++ b/tests/baselines/reference/constDeclarationShadowedByVarDeclaration.errors.txt
@@ -0,0 +1,35 @@
+tests/cases/compiler/constDeclarationShadowedByVarDeclaration.ts(7,9): error TS2451: Cannot redeclare block-scoped variable 'x'.
+tests/cases/compiler/constDeclarationShadowedByVarDeclaration.ts(15,13): error TS2451: Cannot redeclare block-scoped variable 'y'.
+tests/cases/compiler/constDeclarationShadowedByVarDeclaration.ts(22,7): error TS2451: Cannot redeclare block-scoped variable 'z'.
+
+
+==== tests/cases/compiler/constDeclarationShadowedByVarDeclaration.ts (3 errors) ====
+    
+    // Error as declaration of var would cause a write to the const value
+    var x = 0;
+    {
+        const x = 0;
+    
+        var x = 0;
+            ~
+!!! error TS2451: Cannot redeclare block-scoped variable 'x'.
+    }
+    
+    
+    var y = 0;
+    {
+        const y = 0;
+        {
+            var y = 0;
+                ~
+!!! error TS2451: Cannot redeclare block-scoped variable 'y'.
+        }
+    }
+    
+    
+    {
+      const z = 0;
+      var z = 0
+          ~
+!!! error TS2451: Cannot redeclare block-scoped variable 'z'.
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarationShadowedByVarDeclaration2.js b/tests/baselines/reference/constDeclarationShadowedByVarDeclaration2.js
new file mode 100644
index 0000000000000..67d3e688075ad
--- /dev/null
+++ b/tests/baselines/reference/constDeclarationShadowedByVarDeclaration2.js
@@ -0,0 +1,18 @@
+//// [constDeclarationShadowedByVarDeclaration2.ts]
+
+// No errors, const declaration is not shadowed
+function outer() {
+    const x = 0;
+    function inner() {
+        var x = "inner";
+    }
+}
+
+//// [constDeclarationShadowedByVarDeclaration2.js]
+// No errors, const declaration is not shadowed
+function outer() {
+    const x = 0;
+    function inner() {
+        var x = "inner";
+    }
+}
diff --git a/tests/baselines/reference/constDeclarationShadowedByVarDeclaration2.types b/tests/baselines/reference/constDeclarationShadowedByVarDeclaration2.types
new file mode 100644
index 0000000000000..4217db455095a
--- /dev/null
+++ b/tests/baselines/reference/constDeclarationShadowedByVarDeclaration2.types
@@ -0,0 +1,16 @@
+=== tests/cases/compiler/constDeclarationShadowedByVarDeclaration2.ts ===
+
+// No errors, const declaration is not shadowed
+function outer() {
+>outer : () => void
+
+    const x = 0;
+>x : number
+
+    function inner() {
+>inner : () => void
+
+        var x = "inner";
+>x : string
+    }
+}
diff --git a/tests/baselines/reference/constDeclarationShadowedByVarDeclaration3.js b/tests/baselines/reference/constDeclarationShadowedByVarDeclaration3.js
new file mode 100644
index 0000000000000..6f5b898c5ff56
--- /dev/null
+++ b/tests/baselines/reference/constDeclarationShadowedByVarDeclaration3.js
@@ -0,0 +1,21 @@
+//// [constDeclarationShadowedByVarDeclaration3.ts]
+// Ensure only checking for const declarations shadowed by vars
+class Rule {
+    public regex: RegExp = new RegExp('');
+    public name: string = '';
+
+    constructor(name: string) {
+        this.name = name;
+    }
+}
+
+//// [constDeclarationShadowedByVarDeclaration3.js]
+// Ensure only checking for const declarations shadowed by vars
+var Rule = (function () {
+    function Rule(name) {
+        this.regex = new RegExp('');
+        this.name = '';
+        this.name = name;
+    }
+    return Rule;
+})();
diff --git a/tests/baselines/reference/constDeclarationShadowedByVarDeclaration3.types b/tests/baselines/reference/constDeclarationShadowedByVarDeclaration3.types
new file mode 100644
index 0000000000000..89490567f1449
--- /dev/null
+++ b/tests/baselines/reference/constDeclarationShadowedByVarDeclaration3.types
@@ -0,0 +1,25 @@
+=== tests/cases/compiler/constDeclarationShadowedByVarDeclaration3.ts ===
+// Ensure only checking for const declarations shadowed by vars
+class Rule {
+>Rule : Rule
+
+    public regex: RegExp = new RegExp('');
+>regex : RegExp
+>RegExp : RegExp
+>new RegExp('') : RegExp
+>RegExp : { (pattern: string, flags?: string): RegExp; new (pattern: string, flags?: string): RegExp; $1: string; $2: string; $3: string; $4: string; $5: string; $6: string; $7: string; $8: string; $9: string; lastMatch: string; }
+
+    public name: string = '';
+>name : string
+
+    constructor(name: string) {
+>name : string
+
+        this.name = name;
+>this.name = name : string
+>this.name : string
+>this : Rule
+>name : string
+>name : string
+    }
+}
diff --git a/tests/baselines/reference/constDeclarations-access.errors.txt b/tests/baselines/reference/constDeclarations-access.errors.txt
new file mode 100644
index 0000000000000..04b942aec09ef
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-access.errors.txt
@@ -0,0 +1,11 @@
+tests/cases/compiler/file2.ts(1,1): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+
+
+==== tests/cases/compiler/file1.ts (0 errors) ====
+    
+    const x = 0
+    
+==== tests/cases/compiler/file2.ts (1 errors) ====
+    x++;
+    ~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-access2.errors.txt b/tests/baselines/reference/constDeclarations-access2.errors.txt
new file mode 100644
index 0000000000000..6a360e11014e8
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-access2.errors.txt
@@ -0,0 +1,94 @@
+tests/cases/compiler/constDeclarations-access2.ts(5,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(6,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(7,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(8,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(9,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(10,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(11,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(12,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(13,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(14,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(15,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(16,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(18,1): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(19,1): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(20,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(21,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access2.ts(23,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+
+
+==== tests/cases/compiler/constDeclarations-access2.ts (17 errors) ====
+    
+    const x = 0
+    
+    // Errors
+    x = 1;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x += 2;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x -= 3;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x *= 4;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x /= 5;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x %= 6;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x <<= 7;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x >>= 8;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x >>>= 9;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x &= 10;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x |= 11;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    x ^= 12;
+    ~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    
+    x++;
+    ~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    x--;
+    ~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    ++x;
+      ~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    --x;
+      ~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    
+    ++((x));
+      ~~~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    
+    // OK
+    var a = x + 1;
+    
+    function f(v: number) { }
+    f(x);
+    
+    if (x) { }
+    
+    x;
+    (x);
+    
+    -x;
+    +x;
+    
+    x.toString();
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-access3.errors.txt b/tests/baselines/reference/constDeclarations-access3.errors.txt
new file mode 100644
index 0000000000000..577b087dff09a
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-access3.errors.txt
@@ -0,0 +1,102 @@
+tests/cases/compiler/constDeclarations-access3.ts(8,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(9,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(10,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(11,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(12,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(13,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(14,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(15,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(16,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(17,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(18,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(19,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(21,1): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(22,1): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(23,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(24,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(26,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access3.ts(28,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+
+
+==== tests/cases/compiler/constDeclarations-access3.ts (18 errors) ====
+    
+    
+    module M {
+        export const x = 0;
+    }
+    
+    // Errors
+    M.x = 1;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x += 2;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x -= 3;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x *= 4;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x /= 5;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x %= 6;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x <<= 7;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x >>= 8;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x >>>= 9;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x &= 10;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x |= 11;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x ^= 12;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    
+    M.x++;
+    ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    M.x--;
+    ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    ++M.x;
+      ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    --M.x;
+      ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    
+    ++((M.x));
+      ~~~~~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    
+    M["x"] = 0;
+    ~~~~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    
+    // OK
+    var a = M.x + 1;
+    
+    function f(v: number) { }
+    f(M.x);
+    
+    if (M.x) { }
+    
+    M.x;
+    (M.x);
+    
+    -M.x;
+    +M.x;
+    
+    M.x.toString();
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-access4.errors.txt b/tests/baselines/reference/constDeclarations-access4.errors.txt
new file mode 100644
index 0000000000000..9745c0d262497
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-access4.errors.txt
@@ -0,0 +1,102 @@
+tests/cases/compiler/constDeclarations-access4.ts(8,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(9,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(10,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(11,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(12,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(13,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(14,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(15,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(16,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(17,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(18,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(19,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(21,1): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(22,1): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(23,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(24,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(26,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations-access4.ts(28,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+
+
+==== tests/cases/compiler/constDeclarations-access4.ts (18 errors) ====
+    
+    
+    declare module M {
+        const x: number;
+    }
+    
+    // Errors
+    M.x = 1;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x += 2;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x -= 3;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x *= 4;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x /= 5;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x %= 6;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x <<= 7;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x >>= 8;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x >>>= 9;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x &= 10;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x |= 11;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    M.x ^= 12;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    
+    M.x++;
+    ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    M.x--;
+    ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    ++M.x;
+      ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    --M.x;
+      ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    
+    ++((M.x));
+      ~~~~~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    
+    M["x"] = 0;
+    ~~~~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    
+    // OK
+    var a = M.x + 1;
+    
+    function f(v: number) { }
+    f(M.x);
+    
+    if (M.x) { }
+    
+    M.x;
+    (M.x);
+    
+    -M.x;
+    +M.x;
+    
+    M.x.toString();
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-access5.errors.txt b/tests/baselines/reference/constDeclarations-access5.errors.txt
new file mode 100644
index 0000000000000..23200e50ee42b
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-access5.errors.txt
@@ -0,0 +1,103 @@
+tests/cases/compiler/constDeclarations_access_2.ts(4,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(5,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(6,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(7,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(8,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(9,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(10,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(11,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(12,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(13,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(14,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(15,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(17,1): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(18,1): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(19,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(20,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(22,3): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+tests/cases/compiler/constDeclarations_access_2.ts(24,1): error TS2450: Left-hand side of assignment expression cannot be a constant.
+
+
+==== tests/cases/compiler/constDeclarations_access_2.ts (18 errors) ====
+    ///<reference path='constDeclarations_access_1.ts'/>
+    import m = require('constDeclarations_access_1');
+    // Errors
+    m.x = 1;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x += 2;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x -= 3;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x *= 4;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x /= 5;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x %= 6;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x <<= 7;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x >>= 8;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x >>>= 9;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x &= 10;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x |= 11;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m.x ^= 12;
+    ~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    m
+    m.x++;
+    ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    m.x--;
+    ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    ++m.x;
+      ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    --m.x;
+      ~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    
+    ++((m.x));
+      ~~~~~~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    
+    m["x"] = 0;
+    ~~~~~~
+!!! error TS2450: Left-hand side of assignment expression cannot be a constant.
+    
+    // OK
+    var a = m.x + 1;
+    
+    function f(v: number) { }
+    f(m.x);
+    
+    if (m.x) { }
+    
+    m.x;
+    (m.x);
+    
+    -m.x;
+    +m.x;
+    
+    m.x.toString();
+    
+==== tests/cases/compiler/constDeclarations_access_1.ts (0 errors) ====
+    
+    
+    export const x = 0;
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-ambient-errors.errors.txt b/tests/baselines/reference/constDeclarations-ambient-errors.errors.txt
new file mode 100644
index 0000000000000..6e2d00dc4c42c
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-ambient-errors.errors.txt
@@ -0,0 +1,34 @@
+tests/cases/compiler/constDeclarations-ambient-errors.ts(3,27): error TS1039: Initializers are not allowed in ambient contexts.
+tests/cases/compiler/constDeclarations-ambient-errors.ts(4,26): error TS1039: Initializers are not allowed in ambient contexts.
+tests/cases/compiler/constDeclarations-ambient-errors.ts(5,18): error TS1039: Initializers are not allowed in ambient contexts.
+tests/cases/compiler/constDeclarations-ambient-errors.ts(5,37): error TS1039: Initializers are not allowed in ambient contexts.
+tests/cases/compiler/constDeclarations-ambient-errors.ts(5,51): error TS1039: Initializers are not allowed in ambient contexts.
+tests/cases/compiler/constDeclarations-ambient-errors.ts(8,14): error TS1039: Initializers are not allowed in ambient contexts.
+tests/cases/compiler/constDeclarations-ambient-errors.ts(9,22): error TS1039: Initializers are not allowed in ambient contexts.
+
+
+==== tests/cases/compiler/constDeclarations-ambient-errors.ts (7 errors) ====
+    
+    // error: no intialization expected in ambient declarations
+    declare const c1: boolean = true;
+                              ~
+!!! error TS1039: Initializers are not allowed in ambient contexts.
+    declare const c2: number = 0;
+                             ~
+!!! error TS1039: Initializers are not allowed in ambient contexts.
+    declare const c3 = null, c4 :string = "", c5: any = 0;
+                     ~
+!!! error TS1039: Initializers are not allowed in ambient contexts.
+                                        ~
+!!! error TS1039: Initializers are not allowed in ambient contexts.
+                                                      ~
+!!! error TS1039: Initializers are not allowed in ambient contexts.
+    
+    declare module M {
+        const c6 = 0;
+                 ~
+!!! error TS1039: Initializers are not allowed in ambient contexts.
+        const c7: number = 7;
+                         ~
+!!! error TS1039: Initializers are not allowed in ambient contexts.
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-ambient.js b/tests/baselines/reference/constDeclarations-ambient.js
new file mode 100644
index 0000000000000..dd78f73051aa4
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-ambient.js
@@ -0,0 +1,13 @@
+//// [constDeclarations-ambient.ts]
+
+// No error
+declare const c1: boolean;
+declare const c2: number;
+declare const c3, c4 :string, c5: any;
+
+declare module M {
+    const c6;
+    const c7: number;
+}
+
+//// [constDeclarations-ambient.js]
diff --git a/tests/baselines/reference/constDeclarations-ambient.types b/tests/baselines/reference/constDeclarations-ambient.types
new file mode 100644
index 0000000000000..0ab2d4b700a69
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-ambient.types
@@ -0,0 +1,23 @@
+=== tests/cases/compiler/constDeclarations-ambient.ts ===
+
+// No error
+declare const c1: boolean;
+>c1 : boolean
+
+declare const c2: number;
+>c2 : number
+
+declare const c3, c4 :string, c5: any;
+>c3 : any
+>c4 : string
+>c5 : any
+
+declare module M {
+>M : typeof M
+
+    const c6;
+>c6 : any
+
+    const c7: number;
+>c7 : number
+}
diff --git a/tests/baselines/reference/constDeclarations-errors.errors.txt b/tests/baselines/reference/constDeclarations-errors.errors.txt
new file mode 100644
index 0000000000000..d87007474a1a4
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-errors.errors.txt
@@ -0,0 +1,50 @@
+tests/cases/compiler/constDeclarations-errors.ts(3,7): error TS1155: 'const' declarations must be initialized
+tests/cases/compiler/constDeclarations-errors.ts(4,7): error TS1155: 'const' declarations must be initialized
+tests/cases/compiler/constDeclarations-errors.ts(5,7): error TS1155: 'const' declarations must be initialized
+tests/cases/compiler/constDeclarations-errors.ts(5,11): error TS1155: 'const' declarations must be initialized
+tests/cases/compiler/constDeclarations-errors.ts(5,15): error TS1155: 'const' declarations must be initialized
+tests/cases/compiler/constDeclarations-errors.ts(5,27): error TS1155: 'const' declarations must be initialized
+tests/cases/compiler/constDeclarations-errors.ts(8,11): error TS1155: 'const' declarations must be initialized
+tests/cases/compiler/constDeclarations-errors.ts(14,11): error TS1155: 'const' declarations must be initialized
+tests/cases/compiler/constDeclarations-errors.ts(17,20): error TS1155: 'const' declarations must be initialized
+tests/cases/compiler/constDeclarations-errors.ts(11,27): error TS2449: The operand of an increment or decrement operator cannot be a constant.
+
+
+==== tests/cases/compiler/constDeclarations-errors.ts (10 errors) ====
+    
+    // error, missing intialicer
+    const c1;
+          ~~
+!!! error TS1155: 'const' declarations must be initialized
+    const c2: number;
+          ~~
+!!! error TS1155: 'const' declarations must be initialized
+    const c3, c4, c5 :string, c6;  // error, missing initialicer
+          ~~
+!!! error TS1155: 'const' declarations must be initialized
+              ~~
+!!! error TS1155: 'const' declarations must be initialized
+                  ~~
+!!! error TS1155: 'const' declarations must be initialized
+                              ~~
+!!! error TS1155: 'const' declarations must be initialized
+    
+    // error, can not be unintalized
+    for(const c in {}) { }
+              ~
+!!! error TS1155: 'const' declarations must be initialized
+    
+    // error, assigning to a const
+    for(const c8 = 0; c8 < 1; c8++) { }
+                              ~~
+!!! error TS2449: The operand of an increment or decrement operator cannot be a constant.
+    
+    // error, can not be unintalized
+    for(const c9; c9 < 1;) { }
+              ~~
+!!! error TS1155: 'const' declarations must be initialized
+    
+    // error, can not be unintalized
+    for(const c10 = 0, c11; c10 < 1;) { }
+                       ~~~
+!!! error TS1155: 'const' declarations must be initialized
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-es5.errors.txt b/tests/baselines/reference/constDeclarations-es5.errors.txt
new file mode 100644
index 0000000000000..0b830eab05a82
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-es5.errors.txt
@@ -0,0 +1,17 @@
+tests/cases/compiler/constDeclarations-es5.ts(2,1): error TS1154: 'const' declarations are only available when targeting ECMAScript 6 and higher.
+tests/cases/compiler/constDeclarations-es5.ts(3,1): error TS1154: 'const' declarations are only available when targeting ECMAScript 6 and higher.
+tests/cases/compiler/constDeclarations-es5.ts(4,1): error TS1154: 'const' declarations are only available when targeting ECMAScript 6 and higher.
+
+
+==== tests/cases/compiler/constDeclarations-es5.ts (3 errors) ====
+    
+    const z7 = false;
+    ~~~~~~~~~~~~~~~~~
+!!! error TS1154: 'const' declarations are only available when targeting ECMAScript 6 and higher.
+    const z8: number = 23;
+    ~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1154: 'const' declarations are only available when targeting ECMAScript 6 and higher.
+    const z9 = 0, z10 :string = "", z11 = null;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1154: 'const' declarations are only available when targeting ECMAScript 6 and higher.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-invalidContexts.errors.txt b/tests/baselines/reference/constDeclarations-invalidContexts.errors.txt
new file mode 100644
index 0000000000000..745ef305ac6ba
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-invalidContexts.errors.txt
@@ -0,0 +1,66 @@
+tests/cases/compiler/constDeclarations-invalidContexts.ts(4,5): error TS1156: 'const' declarations can only be declared inside a block.
+tests/cases/compiler/constDeclarations-invalidContexts.ts(6,5): error TS1156: 'const' declarations can only be declared inside a block.
+tests/cases/compiler/constDeclarations-invalidContexts.ts(9,5): error TS1156: 'const' declarations can only be declared inside a block.
+tests/cases/compiler/constDeclarations-invalidContexts.ts(12,5): error TS1156: 'const' declarations can only be declared inside a block.
+tests/cases/compiler/constDeclarations-invalidContexts.ts(17,5): error TS1156: 'const' declarations can only be declared inside a block.
+tests/cases/compiler/constDeclarations-invalidContexts.ts(20,5): error TS1156: 'const' declarations can only be declared inside a block.
+tests/cases/compiler/constDeclarations-invalidContexts.ts(23,5): error TS1156: 'const' declarations can only be declared inside a block.
+tests/cases/compiler/constDeclarations-invalidContexts.ts(26,12): error TS1156: 'const' declarations can only be declared inside a block.
+tests/cases/compiler/constDeclarations-invalidContexts.ts(29,29): error TS1156: 'const' declarations can only be declared inside a block.
+tests/cases/compiler/constDeclarations-invalidContexts.ts(16,7): error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+
+
+==== tests/cases/compiler/constDeclarations-invalidContexts.ts (10 errors) ====
+    
+    // Errors, const must be defined inside a block
+    if (true) 
+        const c1 = 0;
+        ~~~~~~~~~~~~~
+!!! error TS1156: 'const' declarations can only be declared inside a block.
+    else 
+        const c2 = 0;
+        ~~~~~~~~~~~~~
+!!! error TS1156: 'const' declarations can only be declared inside a block.
+    
+    while (true) 
+        const c3 = 0;
+        ~~~~~~~~~~~~~
+!!! error TS1156: 'const' declarations can only be declared inside a block.
+    
+    do 
+        const c4 = 0;
+        ~~~~~~~~~~~~~
+!!! error TS1156: 'const' declarations can only be declared inside a block.
+    while (true);
+    
+    var obj;
+    with (obj) 
+          ~~~
+!!! error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+        const c5 = 0;
+        ~~~~~~~~~~~~~
+!!! error TS1156: 'const' declarations can only be declared inside a block.
+    
+    for (var i = 0; i < 10; i++)
+        const c6 = 0;
+        ~~~~~~~~~~~~~
+!!! error TS1156: 'const' declarations can only be declared inside a block.
+    
+    for (var i2 in {}) 
+        const c7 = 0;
+        ~~~~~~~~~~~~~
+!!! error TS1156: 'const' declarations can only be declared inside a block.
+    
+    if (true) 
+        label: const c8 = 0;
+               ~~~~~~~~~~~~~
+!!! error TS1156: 'const' declarations can only be declared inside a block.
+    
+    while (false)
+        label2: label3: label4: const c9 = 0;
+                                ~~~~~~~~~~~~~
+!!! error TS1156: 'const' declarations can only be declared inside a block.
+    
+    
+    
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-scopes.errors.txt b/tests/baselines/reference/constDeclarations-scopes.errors.txt
new file mode 100644
index 0000000000000..138acd9b16d1c
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-scopes.errors.txt
@@ -0,0 +1,153 @@
+tests/cases/compiler/constDeclarations-scopes.ts(28,7): error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+
+
+==== tests/cases/compiler/constDeclarations-scopes.ts (1 errors) ====
+    
+    // global
+    const c = "string";
+    
+    var n: number;
+    
+    // Control flow statements with blocks
+    if (true) { 
+        const c = 0;
+        n = c;
+    }
+    else { 
+        const c = 0;
+        n = c;
+    }
+    
+    while (true) { 
+        const c = 0;
+        n = c;
+    }
+    
+    do { 
+       const c = 0;
+        n = c;
+    } while (true);
+    
+    var obj;
+    with (obj) {
+          ~~~
+!!! error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+        const c = 0;
+        n = c;
+    }
+    
+    for (var i = 0; i < 10; i++) {
+        const c = 0;
+        n = c;
+    }
+    
+    for (var i2 in {}) {
+        const c = 0;
+        n = c;
+    }
+    
+    if (true) {
+        label: const c = 0;
+        n = c;
+    }
+    
+    while (false) {
+        label2: label3: label4: const c = 0;
+        n = c;
+    }
+    
+    // Try/catch/finally
+    try {
+        const c = 0;
+        n = c;
+    }
+    catch (e) {
+        const c = 0;
+        n = c;
+    }
+    finally {
+        const c = 0;
+        n = c;
+    }
+    
+    // Switch
+    switch (0) {
+        case 0:
+            const c = 0;
+            n = c;
+            break;
+    }
+    
+    // blocks
+    {
+        const c = 0;
+        n = c;
+        {
+            const c = false;
+            var b: boolean = c;
+        }
+    }
+    
+    // functions
+    
+    function F() {
+        const c = 0;
+        n = c;
+    }
+    
+    var F2 = () => {
+        const c = 0;
+        n = c;
+    };
+    
+    var F3 = function () {
+        const c = 0;
+        n = c;
+    };
+    
+    // modules
+    module m {
+        const c = 0;
+        n = c;
+    
+        {
+           const c = false;
+           var b2: boolean = c;
+        }
+    }
+    
+    // methods
+    class C {
+        constructor() {
+            const c = 0;
+            n = c;
+        }
+    
+        method() {
+            const c = 0;
+            n = c;
+        }
+    
+        get v() {
+            const c = 0;
+            n = c;
+            return n;
+        }
+    
+        set v(value) {
+            const c = 0;
+            n = c;
+        }
+    }
+    
+    // object literals
+    var o = {
+        f() {
+            const c = 0;
+            n = c;
+        },
+        f2: () => {
+            const c = 0;
+            n = c;
+        }
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-scopes.js b/tests/baselines/reference/constDeclarations-scopes.js
new file mode 100644
index 0000000000000..800dd856422ea
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-scopes.js
@@ -0,0 +1,276 @@
+//// [constDeclarations-scopes.ts]
+
+// global
+const c = "string";
+
+var n: number;
+
+// Control flow statements with blocks
+if (true) { 
+    const c = 0;
+    n = c;
+}
+else { 
+    const c = 0;
+    n = c;
+}
+
+while (true) { 
+    const c = 0;
+    n = c;
+}
+
+do { 
+   const c = 0;
+    n = c;
+} while (true);
+
+var obj;
+with (obj) {
+    const c = 0;
+    n = c;
+}
+
+for (var i = 0; i < 10; i++) {
+    const c = 0;
+    n = c;
+}
+
+for (var i2 in {}) {
+    const c = 0;
+    n = c;
+}
+
+if (true) {
+    label: const c = 0;
+    n = c;
+}
+
+while (false) {
+    label2: label3: label4: const c = 0;
+    n = c;
+}
+
+// Try/catch/finally
+try {
+    const c = 0;
+    n = c;
+}
+catch (e) {
+    const c = 0;
+    n = c;
+}
+finally {
+    const c = 0;
+    n = c;
+}
+
+// Switch
+switch (0) {
+    case 0:
+        const c = 0;
+        n = c;
+        break;
+}
+
+// blocks
+{
+    const c = 0;
+    n = c;
+    {
+        const c = false;
+        var b: boolean = c;
+    }
+}
+
+// functions
+
+function F() {
+    const c = 0;
+    n = c;
+}
+
+var F2 = () => {
+    const c = 0;
+    n = c;
+};
+
+var F3 = function () {
+    const c = 0;
+    n = c;
+};
+
+// modules
+module m {
+    const c = 0;
+    n = c;
+
+    {
+       const c = false;
+       var b2: boolean = c;
+    }
+}
+
+// methods
+class C {
+    constructor() {
+        const c = 0;
+        n = c;
+    }
+
+    method() {
+        const c = 0;
+        n = c;
+    }
+
+    get v() {
+        const c = 0;
+        n = c;
+        return n;
+    }
+
+    set v(value) {
+        const c = 0;
+        n = c;
+    }
+}
+
+// object literals
+var o = {
+    f() {
+        const c = 0;
+        n = c;
+    },
+    f2: () => {
+        const c = 0;
+        n = c;
+    }
+}
+
+//// [constDeclarations-scopes.js]
+// global
+const c = "string";
+var n;
+// Control flow statements with blocks
+if (true) {
+    const c = 0;
+    n = c;
+}
+else {
+    const c = 0;
+    n = c;
+}
+while (true) {
+    const c = 0;
+    n = c;
+}
+do {
+    const c = 0;
+    n = c;
+} while (true);
+var obj;
+with (obj) {
+    const c = 0;
+    n = c;
+}
+for (var i = 0; i < 10; i++) {
+    const c = 0;
+    n = c;
+}
+for (var i2 in {}) {
+    const c = 0;
+    n = c;
+}
+if (true) {
+    label: const c = 0;
+    n = c;
+}
+while (false) {
+    label2: label3: label4: const c = 0;
+    n = c;
+}
+try {
+    const c = 0;
+    n = c;
+}
+catch (e) {
+    const c = 0;
+    n = c;
+}
+finally {
+    const c = 0;
+    n = c;
+}
+switch (0) {
+    case 0:
+        const c = 0;
+        n = c;
+        break;
+}
+{
+    const c = 0;
+    n = c;
+    {
+        const c = false;
+        var b = c;
+    }
+}
+// functions
+function F() {
+    const c = 0;
+    n = c;
+}
+var F2 = function () {
+    const c = 0;
+    n = c;
+};
+var F3 = function () {
+    const c = 0;
+    n = c;
+};
+// modules
+var m;
+(function (m) {
+    const c = 0;
+    n = c;
+    {
+        const c = false;
+        var b2 = c;
+    }
+})(m || (m = {}));
+// methods
+var C = (function () {
+    function C() {
+        const c = 0;
+        n = c;
+    }
+    C.prototype.method = function () {
+        const c = 0;
+        n = c;
+    };
+    Object.defineProperty(C.prototype, "v", {
+        get: function () {
+            const c = 0;
+            n = c;
+            return n;
+        },
+        set: function (value) {
+            const c = 0;
+            n = c;
+        },
+        enumerable: true,
+        configurable: true
+    });
+    return C;
+})();
+// object literals
+var o = {
+    f: function () {
+        const c = 0;
+        n = c;
+    },
+    f2: function () {
+        const c = 0;
+        n = c;
+    }
+};
diff --git a/tests/baselines/reference/constDeclarations-scopes2.js b/tests/baselines/reference/constDeclarations-scopes2.js
new file mode 100644
index 0000000000000..1d0f252ab4f2d
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-scopes2.js
@@ -0,0 +1,27 @@
+//// [constDeclarations-scopes2.ts]
+
+// global
+const c = "string";
+
+var n: number;
+var b: boolean;
+
+// for scope
+for (const c = 0; c < 10; n = c ) {
+    // for block
+    const c = false;
+    b = c;
+}
+
+
+
+//// [constDeclarations-scopes2.js]
+// global
+const c = "string";
+var n;
+var b;
+for (const c = 0; c < 10; n = c) {
+    // for block
+    const c = false;
+    b = c;
+}
diff --git a/tests/baselines/reference/constDeclarations-scopes2.types b/tests/baselines/reference/constDeclarations-scopes2.types
new file mode 100644
index 0000000000000..9609ef8f44b1e
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-scopes2.types
@@ -0,0 +1,32 @@
+=== tests/cases/compiler/constDeclarations-scopes2.ts ===
+
+// global
+const c = "string";
+>c : string
+
+var n: number;
+>n : number
+
+var b: boolean;
+>b : boolean
+
+// for scope
+for (const c = 0; c < 10; n = c ) {
+>c : number
+>c < 10 : boolean
+>c : number
+>n = c : number
+>n : number
+>c : number
+
+    // for block
+    const c = false;
+>c : boolean
+
+    b = c;
+>b = c : boolean
+>b : boolean
+>c : boolean
+}
+
+
diff --git a/tests/baselines/reference/constDeclarations-useBeforeDefinition.errors.txt b/tests/baselines/reference/constDeclarations-useBeforeDefinition.errors.txt
new file mode 100644
index 0000000000000..97cf58c6e9d23
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-useBeforeDefinition.errors.txt
@@ -0,0 +1,21 @@
+tests/cases/compiler/constDeclarations-useBeforeDefinition.ts(3,5): error TS2448: Block-scoped variable 'c1' used before its declaration.
+tests/cases/compiler/constDeclarations-useBeforeDefinition.ts(9,5): error TS2448: Block-scoped variable 'v1' used before its declaration.
+
+
+==== tests/cases/compiler/constDeclarations-useBeforeDefinition.ts (2 errors) ====
+    
+    {
+        c1;
+        ~~
+!!! error TS2448: Block-scoped variable 'c1' used before its declaration.
+        const c1 = 0;
+    }
+    
+    var v1;
+    {
+        v1;
+        ~~
+!!! error TS2448: Block-scoped variable 'v1' used before its declaration.
+        const v1 = 0;
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-useBeforeDefinition2.errors.txt b/tests/baselines/reference/constDeclarations-useBeforeDefinition2.errors.txt
new file mode 100644
index 0000000000000..a4d28f5187857
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-useBeforeDefinition2.errors.txt
@@ -0,0 +1,11 @@
+tests/cases/compiler/file1.ts(2,1): error TS2448: Block-scoped variable 'c' used before its declaration.
+
+
+==== tests/cases/compiler/file1.ts (1 errors) ====
+    
+    c;
+    ~
+!!! error TS2448: Block-scoped variable 'c' used before its declaration.
+    
+==== tests/cases/compiler/file2.ts (0 errors) ====
+    const c = 0;
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-validContexts.errors.txt b/tests/baselines/reference/constDeclarations-validContexts.errors.txt
new file mode 100644
index 0000000000000..7af16a53cbe7e
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-validContexts.errors.txt
@@ -0,0 +1,129 @@
+tests/cases/compiler/constDeclarations-validContexts.ts(20,7): error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+
+
+==== tests/cases/compiler/constDeclarations-validContexts.ts (1 errors) ====
+    
+    
+    // Control flow statements with blocks
+    if (true) { 
+        const c1 = 0;
+    }
+    else { 
+        const c2 = 0;
+    }
+    
+    while (true) { 
+        const c3 = 0;
+    }
+    
+    do { 
+        const c4 = 0;
+    } while (true);
+    
+    var obj;
+    with (obj) {
+          ~~~
+!!! error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+        const c5 = 0;
+    }
+    
+    for (var i = 0; i < 10; i++) {
+        const c6 = 0;
+    }
+    
+    for (var i2 in {}) {
+        const c7 = 0;
+    }
+    
+    if (true) {
+        label: const c8 = 0;
+    }
+    
+    while (false) {
+        label2: label3: label4: const c9 = 0;
+    }
+    
+    // Try/catch/finally
+    try {
+        const c10 = 0;
+    }
+    catch (e) {
+        const c11 = 0;
+    }
+    finally {
+        const c12 = 0;
+    }
+    
+    // Switch
+    switch (0) {
+        case 0:
+            const c13 = 0;
+            break;
+        default:
+            const c14 = 0;
+            break;
+    }
+    
+    // blocks
+    {
+        const c15 = 0;
+        {
+            const c16 = 0
+            label17: const c17 = 0;
+        }
+    }
+    
+    // global
+    const c18 = 0;
+    
+    // functions
+    function F() {
+        const c19 = 0;
+    }
+    
+    var F2 = () => {
+        const c20 = 0;
+    };
+    
+    var F3 = function () {
+        const c21 = 0;
+    };
+    
+    // modules
+    module m {
+        const c22 = 0;
+    
+        {
+              const c23 = 0;
+        }
+    }
+    
+    // methods
+    class C {
+        constructor() {
+            const c24 = 0;
+        }
+    
+        method() {
+            const c25 = 0;
+        }
+    
+        get v() {
+            const c26 = 0;
+            return c26; 
+        }
+    
+        set v(value) {
+            const c27 = value;
+        }
+    }
+    
+    // object literals
+    var o = {
+        f() {
+            const c28 = 0;
+        },
+        f2: () => {
+            const c29 = 0;
+        }
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/constDeclarations-validContexts.js b/tests/baselines/reference/constDeclarations-validContexts.js
new file mode 100644
index 0000000000000..355f39af2f2f9
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations-validContexts.js
@@ -0,0 +1,229 @@
+//// [constDeclarations-validContexts.ts]
+
+
+// Control flow statements with blocks
+if (true) { 
+    const c1 = 0;
+}
+else { 
+    const c2 = 0;
+}
+
+while (true) { 
+    const c3 = 0;
+}
+
+do { 
+    const c4 = 0;
+} while (true);
+
+var obj;
+with (obj) {
+    const c5 = 0;
+}
+
+for (var i = 0; i < 10; i++) {
+    const c6 = 0;
+}
+
+for (var i2 in {}) {
+    const c7 = 0;
+}
+
+if (true) {
+    label: const c8 = 0;
+}
+
+while (false) {
+    label2: label3: label4: const c9 = 0;
+}
+
+// Try/catch/finally
+try {
+    const c10 = 0;
+}
+catch (e) {
+    const c11 = 0;
+}
+finally {
+    const c12 = 0;
+}
+
+// Switch
+switch (0) {
+    case 0:
+        const c13 = 0;
+        break;
+    default:
+        const c14 = 0;
+        break;
+}
+
+// blocks
+{
+    const c15 = 0;
+    {
+        const c16 = 0
+        label17: const c17 = 0;
+    }
+}
+
+// global
+const c18 = 0;
+
+// functions
+function F() {
+    const c19 = 0;
+}
+
+var F2 = () => {
+    const c20 = 0;
+};
+
+var F3 = function () {
+    const c21 = 0;
+};
+
+// modules
+module m {
+    const c22 = 0;
+
+    {
+          const c23 = 0;
+    }
+}
+
+// methods
+class C {
+    constructor() {
+        const c24 = 0;
+    }
+
+    method() {
+        const c25 = 0;
+    }
+
+    get v() {
+        const c26 = 0;
+        return c26; 
+    }
+
+    set v(value) {
+        const c27 = value;
+    }
+}
+
+// object literals
+var o = {
+    f() {
+        const c28 = 0;
+    },
+    f2: () => {
+        const c29 = 0;
+    }
+}
+
+//// [constDeclarations-validContexts.js]
+// Control flow statements with blocks
+if (true) {
+    const c1 = 0;
+}
+else {
+    const c2 = 0;
+}
+while (true) {
+    const c3 = 0;
+}
+do {
+    const c4 = 0;
+} while (true);
+var obj;
+with (obj) {
+    const c5 = 0;
+}
+for (var i = 0; i < 10; i++) {
+    const c6 = 0;
+}
+for (var i2 in {}) {
+    const c7 = 0;
+}
+if (true) {
+    label: const c8 = 0;
+}
+while (false) {
+    label2: label3: label4: const c9 = 0;
+}
+try {
+    const c10 = 0;
+}
+catch (e) {
+    const c11 = 0;
+}
+finally {
+    const c12 = 0;
+}
+switch (0) {
+    case 0:
+        const c13 = 0;
+        break;
+    default:
+        const c14 = 0;
+        break;
+}
+{
+    const c15 = 0;
+    {
+        const c16 = 0;
+        label17: const c17 = 0;
+    }
+}
+// global
+const c18 = 0;
+// functions
+function F() {
+    const c19 = 0;
+}
+var F2 = function () {
+    const c20 = 0;
+};
+var F3 = function () {
+    const c21 = 0;
+};
+// modules
+var m;
+(function (m) {
+    const c22 = 0;
+    {
+        const c23 = 0;
+    }
+})(m || (m = {}));
+// methods
+var C = (function () {
+    function C() {
+        const c24 = 0;
+    }
+    C.prototype.method = function () {
+        const c25 = 0;
+    };
+    Object.defineProperty(C.prototype, "v", {
+        get: function () {
+            const c26 = 0;
+            return c26;
+        },
+        set: function (value) {
+            const c27 = value;
+        },
+        enumerable: true,
+        configurable: true
+    });
+    return C;
+})();
+// object literals
+var o = {
+    f: function () {
+        const c28 = 0;
+    },
+    f2: function () {
+        const c29 = 0;
+    }
+};
diff --git a/tests/baselines/reference/constDeclarations.js b/tests/baselines/reference/constDeclarations.js
new file mode 100644
index 0000000000000..060c0aba61cd6
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations.js
@@ -0,0 +1,30 @@
+//// [constDeclarations.ts]
+
+// No error
+const c1 = false;
+const c2: number = 23;
+const c3 = 0, c4 :string = "", c5 = null;
+
+
+for(const c4 = 0; c4 < 9; ) { break; }
+
+
+for(const c5 = 0, c6 = 0; c5 < c6; ) { break; }
+
+//// [constDeclarations.js]
+// No error
+const c1 = false;
+const c2 = 23;
+const c3 = 0, c4 = "", c5 = null;
+for (const c4 = 0; c4 < 9;) {
+    break;
+}
+for (const c5 = 0, c6 = 0; c5 < c6;) {
+    break;
+}
+
+
+//// [constDeclarations.d.ts]
+declare const c1: boolean;
+declare const c2: number;
+declare const c3: number, c4: string, c5: any;
diff --git a/tests/baselines/reference/constDeclarations.types b/tests/baselines/reference/constDeclarations.types
new file mode 100644
index 0000000000000..e82a2f0035f50
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations.types
@@ -0,0 +1,28 @@
+=== tests/cases/compiler/constDeclarations.ts ===
+
+// No error
+const c1 = false;
+>c1 : boolean
+
+const c2: number = 23;
+>c2 : number
+
+const c3 = 0, c4 :string = "", c5 = null;
+>c3 : number
+>c4 : string
+>c5 : any
+
+
+for(const c4 = 0; c4 < 9; ) { break; }
+>c4 : number
+>c4 < 9 : boolean
+>c4 : number
+
+
+for(const c5 = 0, c6 = 0; c5 < c6; ) { break; }
+>c5 : number
+>c6 : number
+>c5 < c6 : boolean
+>c5 : number
+>c6 : number
+
diff --git a/tests/baselines/reference/constDeclarations2.js b/tests/baselines/reference/constDeclarations2.js
new file mode 100644
index 0000000000000..e4ee67ebdcdd0
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations2.js
@@ -0,0 +1,26 @@
+//// [constDeclarations2.ts]
+
+// No error
+module M {
+    export const c1 = false;
+    export const c2: number = 23;
+    export const c3 = 0, c4 :string = "", c5 = null;
+}
+
+
+//// [constDeclarations2.js]
+// No error
+var M;
+(function (M) {
+    M.c1 = false;
+    M.c2 = 23;
+    M.c3 = 0, M.c4 = "", M.c5 = null;
+})(M || (M = {}));
+
+
+//// [constDeclarations2.d.ts]
+declare module M {
+    const c1: boolean;
+    const c2: number;
+    const c3: number, c4: string, c5: any;
+}
diff --git a/tests/baselines/reference/constDeclarations2.types b/tests/baselines/reference/constDeclarations2.types
new file mode 100644
index 0000000000000..c81eca96b0dd0
--- /dev/null
+++ b/tests/baselines/reference/constDeclarations2.types
@@ -0,0 +1,18 @@
+=== tests/cases/compiler/constDeclarations2.ts ===
+
+// No error
+module M {
+>M : typeof M
+
+    export const c1 = false;
+>c1 : boolean
+
+    export const c2: number = 23;
+>c2 : number
+
+    export const c3 = 0, c4 :string = "", c5 = null;
+>c3 : number
+>c4 : string
+>c5 : any
+}
+
diff --git a/tests/baselines/reference/enumIdentifierLiterals.errors.txt b/tests/baselines/reference/enumIdentifierLiterals.errors.txt
index 60d8ed81f84e4..dbf8734ea73bd 100644
--- a/tests/baselines/reference/enumIdentifierLiterals.errors.txt
+++ b/tests/baselines/reference/enumIdentifierLiterals.errors.txt
@@ -1,22 +1,22 @@
-tests/cases/compiler/enumIdentifierLiterals.ts(2,5): error TS1151: An enum member cannot have a numeric name.
-tests/cases/compiler/enumIdentifierLiterals.ts(3,5): error TS1151: An enum member cannot have a numeric name.
-tests/cases/compiler/enumIdentifierLiterals.ts(4,5): error TS1151: An enum member cannot have a numeric name.
-tests/cases/compiler/enumIdentifierLiterals.ts(6,5): error TS1151: An enum member cannot have a numeric name.
+tests/cases/compiler/enumIdentifierLiterals.ts(2,5): error TS2452: An enum member cannot have a numeric name.
+tests/cases/compiler/enumIdentifierLiterals.ts(3,5): error TS2452: An enum member cannot have a numeric name.
+tests/cases/compiler/enumIdentifierLiterals.ts(4,5): error TS2452: An enum member cannot have a numeric name.
+tests/cases/compiler/enumIdentifierLiterals.ts(6,5): error TS2452: An enum member cannot have a numeric name.
 
 
 ==== tests/cases/compiler/enumIdentifierLiterals.ts (4 errors) ====
     enum Nums {
         1.0,
         ~~~
-!!! error TS1151: An enum member cannot have a numeric name.
+!!! error TS2452: An enum member cannot have a numeric name.
         11e-1,
         ~~~~~
-!!! error TS1151: An enum member cannot have a numeric name.
+!!! error TS2452: An enum member cannot have a numeric name.
         0.12e1,
         ~~~~~~
-!!! error TS1151: An enum member cannot have a numeric name.
+!!! error TS2452: An enum member cannot have a numeric name.
         "13e-1",
         0xF00D
         ~~~~~~
-!!! error TS1151: An enum member cannot have a numeric name.
+!!! error TS2452: An enum member cannot have a numeric name.
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/es6-amd.js b/tests/baselines/reference/es6-amd.js
new file mode 100644
index 0000000000000..0cce3af04463a
--- /dev/null
+++ b/tests/baselines/reference/es6-amd.js
@@ -0,0 +1,31 @@
+//// [es6-amd.ts]
+
+class A
+{
+    constructor ()
+    {
+
+    }
+
+    public B()
+    {
+        return 42;
+    }
+}
+
+//// [es6-amd.js]
+var A = (function () {
+    function A() {
+    }
+    A.prototype.B = function () {
+        return 42;
+    };
+    return A;
+})();
+//# sourceMappingURL=es6-amd.js.map
+
+//// [es6-amd.d.ts]
+declare class A {
+    constructor();
+    B(): number;
+}
diff --git a/tests/baselines/reference/es6-amd.js.map b/tests/baselines/reference/es6-amd.js.map
new file mode 100644
index 0000000000000..7371ba578bd1d
--- /dev/null
+++ b/tests/baselines/reference/es6-amd.js.map
@@ -0,0 +1,2 @@
+//// [es6-amd.js.map]
+{"version":3,"file":"es6-amd.js","sourceRoot":"","sources":["es6-amd.ts"],"names":["A","A.constructor","A.B"],"mappings":"AACA,IAAM,CAAC;IAEHA,SAFEA,CAACA;IAKHC,CAACA;IAEMD,aAACA,GAARA;QAEIE,MAAMA,CAACA,EAAEA,CAACA;IACdA,CAACA;IACLF,QAACA;AAADA,CAACA,AAXD,IAWC"}
\ No newline at end of file
diff --git a/tests/baselines/reference/es6-amd.sourcemap.txt b/tests/baselines/reference/es6-amd.sourcemap.txt
new file mode 100644
index 0000000000000..070a35703e173
--- /dev/null
+++ b/tests/baselines/reference/es6-amd.sourcemap.txt
@@ -0,0 +1,128 @@
+===================================================================
+JsFile: es6-amd.js
+mapUrl: es6-amd.js.map
+sourceRoot: 
+sources: es6-amd.ts
+===================================================================
+-------------------------------------------------------------------
+emittedFile:tests/cases/compiler/es6-amd.js
+sourceFile:es6-amd.ts
+-------------------------------------------------------------------
+>>>var A = (function () {
+1 >
+2 >^^^^
+3 >    ^
+4 >     ^^^^^^^^^^^^^^->
+1 >
+  >
+2 >class 
+3 >    A
+1 >Emitted(1, 1) Source(2, 1) + SourceIndex(0)
+2 >Emitted(1, 5) Source(2, 7) + SourceIndex(0)
+3 >Emitted(1, 6) Source(2, 8) + SourceIndex(0)
+---
+>>>    function A() {
+1->^^^^
+2 >    ^^^^^^^^^
+3 >             ^
+1->
+  >{
+  >    
+2 >    
+3 >             A
+1->Emitted(2, 5) Source(4, 5) + SourceIndex(0) name (A)
+2 >Emitted(2, 14) Source(2, 7) + SourceIndex(0) name (A)
+3 >Emitted(2, 15) Source(2, 8) + SourceIndex(0) name (A)
+---
+>>>    }
+1 >^^^^
+2 >    ^
+3 >     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^->
+1 >
+  >{
+  >    constructor ()
+  >    {
+  >
+  >    
+2 >    }
+1 >Emitted(3, 5) Source(7, 5) + SourceIndex(0) name (A.constructor)
+2 >Emitted(3, 6) Source(7, 6) + SourceIndex(0) name (A.constructor)
+---
+>>>    A.prototype.B = function () {
+1->^^^^
+2 >    ^^^^^^^^^^^^^
+3 >                 ^^^
+1->
+  >
+  >    public 
+2 >    B
+3 >                 
+1->Emitted(4, 5) Source(9, 12) + SourceIndex(0) name (A)
+2 >Emitted(4, 18) Source(9, 13) + SourceIndex(0) name (A)
+3 >Emitted(4, 21) Source(9, 5) + SourceIndex(0) name (A)
+---
+>>>        return 42;
+1 >^^^^^^^^
+2 >        ^^^^^^
+3 >              ^
+4 >               ^^
+5 >                 ^
+1 >public B()
+  >    {
+  >        
+2 >        return
+3 >               
+4 >               42
+5 >                 ;
+1 >Emitted(5, 9) Source(11, 9) + SourceIndex(0) name (A.B)
+2 >Emitted(5, 15) Source(11, 15) + SourceIndex(0) name (A.B)
+3 >Emitted(5, 16) Source(11, 16) + SourceIndex(0) name (A.B)
+4 >Emitted(5, 18) Source(11, 18) + SourceIndex(0) name (A.B)
+5 >Emitted(5, 19) Source(11, 19) + SourceIndex(0) name (A.B)
+---
+>>>    };
+1 >^^^^
+2 >    ^
+3 >     ^^^^^^^^^->
+1 >
+  >    
+2 >    }
+1 >Emitted(6, 5) Source(12, 5) + SourceIndex(0) name (A.B)
+2 >Emitted(6, 6) Source(12, 6) + SourceIndex(0) name (A.B)
+---
+>>>    return A;
+1->^^^^
+2 >    ^^^^^^^^
+1->
+  >
+2 >    }
+1->Emitted(7, 5) Source(13, 1) + SourceIndex(0) name (A)
+2 >Emitted(7, 13) Source(13, 2) + SourceIndex(0) name (A)
+---
+>>>})();
+1 >
+2 >^
+3 > 
+4 > ^^^^
+5 >     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^->
+1 >
+2 >}
+3 > 
+4 > class A
+  > {
+  >     constructor ()
+  >     {
+  > 
+  >     }
+  > 
+  >     public B()
+  >     {
+  >         return 42;
+  >     }
+  > }
+1 >Emitted(8, 1) Source(13, 1) + SourceIndex(0) name (A)
+2 >Emitted(8, 2) Source(13, 2) + SourceIndex(0) name (A)
+3 >Emitted(8, 2) Source(2, 1) + SourceIndex(0)
+4 >Emitted(8, 6) Source(13, 2) + SourceIndex(0)
+---
+>>>//# sourceMappingURL=es6-amd.js.map
\ No newline at end of file
diff --git a/tests/baselines/reference/es6-amd.types b/tests/baselines/reference/es6-amd.types
new file mode 100644
index 0000000000000..62815911f7f97
--- /dev/null
+++ b/tests/baselines/reference/es6-amd.types
@@ -0,0 +1,16 @@
+=== tests/cases/compiler/es6-amd.ts ===
+
+class A
+>A : A
+{
+    constructor ()
+    {
+
+    }
+
+    public B()
+>B : () => number
+    {
+        return 42;
+    }
+}
diff --git a/tests/baselines/reference/es6-declaration-amd.js b/tests/baselines/reference/es6-declaration-amd.js
new file mode 100644
index 0000000000000..471f96b223d1a
--- /dev/null
+++ b/tests/baselines/reference/es6-declaration-amd.js
@@ -0,0 +1,31 @@
+//// [es6-declaration-amd.ts]
+
+class A
+{
+    constructor ()
+    {
+
+    }
+
+    public B()
+    {
+        return 42;
+    }
+}
+
+//// [es6-declaration-amd.js]
+var A = (function () {
+    function A() {
+    }
+    A.prototype.B = function () {
+        return 42;
+    };
+    return A;
+})();
+//# sourceMappingURL=es6-declaration-amd.js.map
+
+//// [es6-declaration-amd.d.ts]
+declare class A {
+    constructor();
+    B(): number;
+}
diff --git a/tests/baselines/reference/es6-declaration-amd.js.map b/tests/baselines/reference/es6-declaration-amd.js.map
new file mode 100644
index 0000000000000..0987f9478e99e
--- /dev/null
+++ b/tests/baselines/reference/es6-declaration-amd.js.map
@@ -0,0 +1,2 @@
+//// [es6-declaration-amd.js.map]
+{"version":3,"file":"es6-declaration-amd.js","sourceRoot":"","sources":["es6-declaration-amd.ts"],"names":["A","A.constructor","A.B"],"mappings":"AACA,IAAM,CAAC;IAEHA,SAFEA,CAACA;IAKHC,CAACA;IAEMD,aAACA,GAARA;QAEIE,MAAMA,CAACA,EAAEA,CAACA;IACdA,CAACA;IACLF,QAACA;AAADA,CAACA,AAXD,IAWC"}
\ No newline at end of file
diff --git a/tests/baselines/reference/es6-declaration-amd.sourcemap.txt b/tests/baselines/reference/es6-declaration-amd.sourcemap.txt
new file mode 100644
index 0000000000000..1fc0b5f05fead
--- /dev/null
+++ b/tests/baselines/reference/es6-declaration-amd.sourcemap.txt
@@ -0,0 +1,128 @@
+===================================================================
+JsFile: es6-declaration-amd.js
+mapUrl: es6-declaration-amd.js.map
+sourceRoot: 
+sources: es6-declaration-amd.ts
+===================================================================
+-------------------------------------------------------------------
+emittedFile:tests/cases/compiler/es6-declaration-amd.js
+sourceFile:es6-declaration-amd.ts
+-------------------------------------------------------------------
+>>>var A = (function () {
+1 >
+2 >^^^^
+3 >    ^
+4 >     ^^^^^^^^^^^^^^->
+1 >
+  >
+2 >class 
+3 >    A
+1 >Emitted(1, 1) Source(2, 1) + SourceIndex(0)
+2 >Emitted(1, 5) Source(2, 7) + SourceIndex(0)
+3 >Emitted(1, 6) Source(2, 8) + SourceIndex(0)
+---
+>>>    function A() {
+1->^^^^
+2 >    ^^^^^^^^^
+3 >             ^
+1->
+  >{
+  >    
+2 >    
+3 >             A
+1->Emitted(2, 5) Source(4, 5) + SourceIndex(0) name (A)
+2 >Emitted(2, 14) Source(2, 7) + SourceIndex(0) name (A)
+3 >Emitted(2, 15) Source(2, 8) + SourceIndex(0) name (A)
+---
+>>>    }
+1 >^^^^
+2 >    ^
+3 >     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^->
+1 >
+  >{
+  >    constructor ()
+  >    {
+  >
+  >    
+2 >    }
+1 >Emitted(3, 5) Source(7, 5) + SourceIndex(0) name (A.constructor)
+2 >Emitted(3, 6) Source(7, 6) + SourceIndex(0) name (A.constructor)
+---
+>>>    A.prototype.B = function () {
+1->^^^^
+2 >    ^^^^^^^^^^^^^
+3 >                 ^^^
+1->
+  >
+  >    public 
+2 >    B
+3 >                 
+1->Emitted(4, 5) Source(9, 12) + SourceIndex(0) name (A)
+2 >Emitted(4, 18) Source(9, 13) + SourceIndex(0) name (A)
+3 >Emitted(4, 21) Source(9, 5) + SourceIndex(0) name (A)
+---
+>>>        return 42;
+1 >^^^^^^^^
+2 >        ^^^^^^
+3 >              ^
+4 >               ^^
+5 >                 ^
+1 >public B()
+  >    {
+  >        
+2 >        return
+3 >               
+4 >               42
+5 >                 ;
+1 >Emitted(5, 9) Source(11, 9) + SourceIndex(0) name (A.B)
+2 >Emitted(5, 15) Source(11, 15) + SourceIndex(0) name (A.B)
+3 >Emitted(5, 16) Source(11, 16) + SourceIndex(0) name (A.B)
+4 >Emitted(5, 18) Source(11, 18) + SourceIndex(0) name (A.B)
+5 >Emitted(5, 19) Source(11, 19) + SourceIndex(0) name (A.B)
+---
+>>>    };
+1 >^^^^
+2 >    ^
+3 >     ^^^^^^^^^->
+1 >
+  >    
+2 >    }
+1 >Emitted(6, 5) Source(12, 5) + SourceIndex(0) name (A.B)
+2 >Emitted(6, 6) Source(12, 6) + SourceIndex(0) name (A.B)
+---
+>>>    return A;
+1->^^^^
+2 >    ^^^^^^^^
+1->
+  >
+2 >    }
+1->Emitted(7, 5) Source(13, 1) + SourceIndex(0) name (A)
+2 >Emitted(7, 13) Source(13, 2) + SourceIndex(0) name (A)
+---
+>>>})();
+1 >
+2 >^
+3 > 
+4 > ^^^^
+5 >     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^->
+1 >
+2 >}
+3 > 
+4 > class A
+  > {
+  >     constructor ()
+  >     {
+  > 
+  >     }
+  > 
+  >     public B()
+  >     {
+  >         return 42;
+  >     }
+  > }
+1 >Emitted(8, 1) Source(13, 1) + SourceIndex(0) name (A)
+2 >Emitted(8, 2) Source(13, 2) + SourceIndex(0) name (A)
+3 >Emitted(8, 2) Source(2, 1) + SourceIndex(0)
+4 >Emitted(8, 6) Source(13, 2) + SourceIndex(0)
+---
+>>>//# sourceMappingURL=es6-declaration-amd.js.map
\ No newline at end of file
diff --git a/tests/baselines/reference/es6-declaration-amd.types b/tests/baselines/reference/es6-declaration-amd.types
new file mode 100644
index 0000000000000..e275fc5243961
--- /dev/null
+++ b/tests/baselines/reference/es6-declaration-amd.types
@@ -0,0 +1,16 @@
+=== tests/cases/compiler/es6-declaration-amd.ts ===
+
+class A
+>A : A
+{
+    constructor ()
+    {
+
+    }
+
+    public B()
+>B : () => number
+    {
+        return 42;
+    }
+}
diff --git a/tests/baselines/reference/es6-sourcemap-amd.js b/tests/baselines/reference/es6-sourcemap-amd.js
new file mode 100644
index 0000000000000..805e56cf830d0
--- /dev/null
+++ b/tests/baselines/reference/es6-sourcemap-amd.js
@@ -0,0 +1,25 @@
+//// [es6-sourcemap-amd.ts]
+
+class A
+{
+    constructor ()
+    {
+
+    }
+
+    public B()
+    {
+        return 42;
+    }
+}
+
+//// [es6-sourcemap-amd.js]
+var A = (function () {
+    function A() {
+    }
+    A.prototype.B = function () {
+        return 42;
+    };
+    return A;
+})();
+//# sourceMappingURL=es6-sourcemap-amd.js.map
\ No newline at end of file
diff --git a/tests/baselines/reference/es6-sourcemap-amd.js.map b/tests/baselines/reference/es6-sourcemap-amd.js.map
new file mode 100644
index 0000000000000..689f0447fa8db
--- /dev/null
+++ b/tests/baselines/reference/es6-sourcemap-amd.js.map
@@ -0,0 +1,2 @@
+//// [es6-sourcemap-amd.js.map]
+{"version":3,"file":"es6-sourcemap-amd.js","sourceRoot":"","sources":["es6-sourcemap-amd.ts"],"names":["A","A.constructor","A.B"],"mappings":"AACA,IAAM,CAAC;IAEHA,SAFEA,CAACA;IAKHC,CAACA;IAEMD,aAACA,GAARA;QAEIE,MAAMA,CAACA,EAAEA,CAACA;IACdA,CAACA;IACLF,QAACA;AAADA,CAACA,AAXD,IAWC"}
\ No newline at end of file
diff --git a/tests/baselines/reference/es6-sourcemap-amd.sourcemap.txt b/tests/baselines/reference/es6-sourcemap-amd.sourcemap.txt
new file mode 100644
index 0000000000000..09abb195987c1
--- /dev/null
+++ b/tests/baselines/reference/es6-sourcemap-amd.sourcemap.txt
@@ -0,0 +1,128 @@
+===================================================================
+JsFile: es6-sourcemap-amd.js
+mapUrl: es6-sourcemap-amd.js.map
+sourceRoot: 
+sources: es6-sourcemap-amd.ts
+===================================================================
+-------------------------------------------------------------------
+emittedFile:tests/cases/compiler/es6-sourcemap-amd.js
+sourceFile:es6-sourcemap-amd.ts
+-------------------------------------------------------------------
+>>>var A = (function () {
+1 >
+2 >^^^^
+3 >    ^
+4 >     ^^^^^^^^^^^^^^->
+1 >
+  >
+2 >class 
+3 >    A
+1 >Emitted(1, 1) Source(2, 1) + SourceIndex(0)
+2 >Emitted(1, 5) Source(2, 7) + SourceIndex(0)
+3 >Emitted(1, 6) Source(2, 8) + SourceIndex(0)
+---
+>>>    function A() {
+1->^^^^
+2 >    ^^^^^^^^^
+3 >             ^
+1->
+  >{
+  >    
+2 >    
+3 >             A
+1->Emitted(2, 5) Source(4, 5) + SourceIndex(0) name (A)
+2 >Emitted(2, 14) Source(2, 7) + SourceIndex(0) name (A)
+3 >Emitted(2, 15) Source(2, 8) + SourceIndex(0) name (A)
+---
+>>>    }
+1 >^^^^
+2 >    ^
+3 >     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^->
+1 >
+  >{
+  >    constructor ()
+  >    {
+  >
+  >    
+2 >    }
+1 >Emitted(3, 5) Source(7, 5) + SourceIndex(0) name (A.constructor)
+2 >Emitted(3, 6) Source(7, 6) + SourceIndex(0) name (A.constructor)
+---
+>>>    A.prototype.B = function () {
+1->^^^^
+2 >    ^^^^^^^^^^^^^
+3 >                 ^^^
+1->
+  >
+  >    public 
+2 >    B
+3 >                 
+1->Emitted(4, 5) Source(9, 12) + SourceIndex(0) name (A)
+2 >Emitted(4, 18) Source(9, 13) + SourceIndex(0) name (A)
+3 >Emitted(4, 21) Source(9, 5) + SourceIndex(0) name (A)
+---
+>>>        return 42;
+1 >^^^^^^^^
+2 >        ^^^^^^
+3 >              ^
+4 >               ^^
+5 >                 ^
+1 >public B()
+  >    {
+  >        
+2 >        return
+3 >               
+4 >               42
+5 >                 ;
+1 >Emitted(5, 9) Source(11, 9) + SourceIndex(0) name (A.B)
+2 >Emitted(5, 15) Source(11, 15) + SourceIndex(0) name (A.B)
+3 >Emitted(5, 16) Source(11, 16) + SourceIndex(0) name (A.B)
+4 >Emitted(5, 18) Source(11, 18) + SourceIndex(0) name (A.B)
+5 >Emitted(5, 19) Source(11, 19) + SourceIndex(0) name (A.B)
+---
+>>>    };
+1 >^^^^
+2 >    ^
+3 >     ^^^^^^^^^->
+1 >
+  >    
+2 >    }
+1 >Emitted(6, 5) Source(12, 5) + SourceIndex(0) name (A.B)
+2 >Emitted(6, 6) Source(12, 6) + SourceIndex(0) name (A.B)
+---
+>>>    return A;
+1->^^^^
+2 >    ^^^^^^^^
+1->
+  >
+2 >    }
+1->Emitted(7, 5) Source(13, 1) + SourceIndex(0) name (A)
+2 >Emitted(7, 13) Source(13, 2) + SourceIndex(0) name (A)
+---
+>>>})();
+1 >
+2 >^
+3 > 
+4 > ^^^^
+5 >     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^->
+1 >
+2 >}
+3 > 
+4 > class A
+  > {
+  >     constructor ()
+  >     {
+  > 
+  >     }
+  > 
+  >     public B()
+  >     {
+  >         return 42;
+  >     }
+  > }
+1 >Emitted(8, 1) Source(13, 1) + SourceIndex(0) name (A)
+2 >Emitted(8, 2) Source(13, 2) + SourceIndex(0) name (A)
+3 >Emitted(8, 2) Source(2, 1) + SourceIndex(0)
+4 >Emitted(8, 6) Source(13, 2) + SourceIndex(0)
+---
+>>>//# sourceMappingURL=es6-sourcemap-amd.js.map
\ No newline at end of file
diff --git a/tests/baselines/reference/es6-sourcemap-amd.types b/tests/baselines/reference/es6-sourcemap-amd.types
new file mode 100644
index 0000000000000..661ab2e7cddfc
--- /dev/null
+++ b/tests/baselines/reference/es6-sourcemap-amd.types
@@ -0,0 +1,16 @@
+=== tests/cases/compiler/es6-sourcemap-amd.ts ===
+
+class A
+>A : A
+{
+    constructor ()
+    {
+
+    }
+
+    public B()
+>B : () => number
+    {
+        return 42;
+    }
+}
diff --git a/tests/baselines/reference/functionTypeArgumentArrayAssignment.errors.txt b/tests/baselines/reference/functionTypeArgumentArrayAssignment.errors.txt
deleted file mode 100644
index 9897286a62438..0000000000000
--- a/tests/baselines/reference/functionTypeArgumentArrayAssignment.errors.txt
+++ /dev/null
@@ -1,15 +0,0 @@
-tests/cases/compiler/functionTypeArgumentArrayAssignment.ts(3,2): error TS2300: Duplicate identifier 'length'.
-
-
-==== tests/cases/compiler/functionTypeArgumentArrayAssignment.ts (1 errors) ====
-    interface Array<T> {
-    	foo: T;
-    	length: number;
-    	~~~~~~
-!!! error TS2300: Duplicate identifier 'length'.
-    }
-    
-    function map<U>() {
-    var ys: U[] = [];
-    }
-    
\ No newline at end of file
diff --git a/tests/baselines/reference/functionTypeArgumentArrayAssignment.js b/tests/baselines/reference/functionTypeArgumentArrayAssignment.js
index 9569c4566d818..38188c3505a83 100644
--- a/tests/baselines/reference/functionTypeArgumentArrayAssignment.js
+++ b/tests/baselines/reference/functionTypeArgumentArrayAssignment.js
@@ -1,15 +1,20 @@
 //// [functionTypeArgumentArrayAssignment.ts]
-interface Array<T> {
-	foo: T;
-	length: number;
-}
+module test {
+    interface Array<T> {
+        foo: T;
+        length: number;
+    }
 
-function map<U>() {
-var ys: U[] = [];
+    function map<U>() {
+        var ys: U[] = [];
+    }
 }
 
 
 //// [functionTypeArgumentArrayAssignment.js]
-function map() {
-    var ys = [];
-}
+var test;
+(function (test) {
+    function map() {
+        var ys = [];
+    }
+})(test || (test = {}));
diff --git a/tests/baselines/reference/functionTypeArgumentArrayAssignment.types b/tests/baselines/reference/functionTypeArgumentArrayAssignment.types
new file mode 100644
index 0000000000000..588dfd506ef9e
--- /dev/null
+++ b/tests/baselines/reference/functionTypeArgumentArrayAssignment.types
@@ -0,0 +1,27 @@
+=== tests/cases/compiler/functionTypeArgumentArrayAssignment.ts ===
+module test {
+>test : typeof test
+
+    interface Array<T> {
+>Array : Array<T>
+>T : T
+
+        foo: T;
+>foo : T
+>T : T
+
+        length: number;
+>length : number
+    }
+
+    function map<U>() {
+>map : <U>() => void
+>U : U
+
+        var ys: U[] = [];
+>ys : U[]
+>U : U
+>[] : undefined[]
+    }
+}
+
diff --git a/tests/baselines/reference/instanceofOperator.errors.txt b/tests/baselines/reference/instanceofOperator.errors.txt
index 15d5518874141..2fa517c53be8b 100644
--- a/tests/baselines/reference/instanceofOperator.errors.txt
+++ b/tests/baselines/reference/instanceofOperator.errors.txt
@@ -1,43 +1,42 @@
-tests/cases/compiler/instanceofOperator.ts(6,7): error TS2300: Duplicate identifier 'Object'.
-tests/cases/compiler/instanceofOperator.ts(11,1): error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
-tests/cases/compiler/instanceofOperator.ts(14,16): error TS2359: The right-hand side of an 'instanceof' expression must be of type 'any' or of a type assignable to the 'Function' interface type.
-tests/cases/compiler/instanceofOperator.ts(15,19): error TS2359: The right-hand side of an 'instanceof' expression must be of type 'any' or of a type assignable to the 'Function' interface type.
-tests/cases/compiler/instanceofOperator.ts(18,1): error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
-tests/cases/compiler/instanceofOperator.ts(20,1): error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
+tests/cases/compiler/instanceofOperator.ts(12,5): error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
+tests/cases/compiler/instanceofOperator.ts(15,20): error TS2359: The right-hand side of an 'instanceof' expression must be of type 'any' or of a type assignable to the 'Function' interface type.
+tests/cases/compiler/instanceofOperator.ts(16,23): error TS2359: The right-hand side of an 'instanceof' expression must be of type 'any' or of a type assignable to the 'Function' interface type.
+tests/cases/compiler/instanceofOperator.ts(19,5): error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
+tests/cases/compiler/instanceofOperator.ts(21,5): error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
 
 
-==== tests/cases/compiler/instanceofOperator.ts (6 errors) ====
+==== tests/cases/compiler/instanceofOperator.ts (5 errors) ====
     // Spec:
     // The instanceof operator requires the left operand to be of type Any or an object type, and the right 
     // operand to be of type Any or a subtype of the ‘Function’ interface type. The result is always of the 
     // Boolean primitive type.
     
-    class Object { }
-          ~~~~~~
-!!! error TS2300: Duplicate identifier 'Object'.
-    var obj: Object;
+    module test {
+        class Object { }
+        var obj: Object;
     
     
     
-    4 instanceof null; 
-    ~
+        4 instanceof null;
+        ~
 !!! error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
     
-    // Error and should be error
-    obj instanceof 4;
-                   ~
+        // Error and should be error
+        obj instanceof 4;
+                       ~
 !!! error TS2359: The right-hand side of an 'instanceof' expression must be of type 'any' or of a type assignable to the 'Function' interface type.
-    Object instanceof obj;
-                      ~~~
+        Object instanceof obj;
+                          ~~~
 !!! error TS2359: The right-hand side of an 'instanceof' expression must be of type 'any' or of a type assignable to the 'Function' interface type.
     
-    // Error on left hand side
-    null instanceof null;
-    ~~~~
+        // Error on left hand side
+        null instanceof null;
+        ~~~~
 !!! error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
-    obj instanceof Object;
-    undefined instanceof undefined;
-    ~~~~~~~~~
+        obj instanceof Object;
+        undefined instanceof undefined;
+        ~~~~~~~~~
 !!! error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
+    }
     
     
\ No newline at end of file
diff --git a/tests/baselines/reference/instanceofOperator.js b/tests/baselines/reference/instanceofOperator.js
index 7620c3e83f4fc..3c6970b66a4f1 100644
--- a/tests/baselines/reference/instanceofOperator.js
+++ b/tests/baselines/reference/instanceofOperator.js
@@ -4,21 +4,23 @@
 // operand to be of type Any or a subtype of the ‘Function’ interface type. The result is always of the 
 // Boolean primitive type.
 
-class Object { }
-var obj: Object;
+module test {
+    class Object { }
+    var obj: Object;
 
 
 
-4 instanceof null; 
+    4 instanceof null;
 
-// Error and should be error
-obj instanceof 4;
-Object instanceof obj;
+    // Error and should be error
+    obj instanceof 4;
+    Object instanceof obj;
 
-// Error on left hand side
-null instanceof null;
-obj instanceof Object;
-undefined instanceof undefined;
+    // Error on left hand side
+    null instanceof null;
+    obj instanceof Object;
+    undefined instanceof undefined;
+}
 
 
 
@@ -27,17 +29,20 @@ undefined instanceof undefined;
 // The instanceof operator requires the left operand to be of type Any or an object type, and the right 
 // operand to be of type Any or a subtype of the ‘Function’ interface type. The result is always of the 
 // Boolean primitive type.
-var Object = (function () {
-    function Object() {
-    }
-    return Object;
-})();
-var obj;
-4 instanceof null;
-// Error and should be error
-obj instanceof 4;
-Object instanceof obj;
-// Error on left hand side
-null instanceof null;
-obj instanceof Object;
-undefined instanceof undefined;
+var test;
+(function (test) {
+    var Object = (function () {
+        function Object() {
+        }
+        return Object;
+    })();
+    var obj;
+    4 instanceof null;
+    // Error and should be error
+    obj instanceof 4;
+    Object instanceof obj;
+    // Error on left hand side
+    null instanceof null;
+    obj instanceof Object;
+    undefined instanceof undefined;
+})(test || (test = {}));
diff --git a/tests/baselines/reference/letDeclarations-access.js b/tests/baselines/reference/letDeclarations-access.js
new file mode 100644
index 0000000000000..404c287631079
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-access.js
@@ -0,0 +1,70 @@
+//// [letDeclarations-access.ts]
+
+let x = 0
+
+// No errors
+
+x = 1;
+x += 2;
+x -= 3;
+x *= 4;
+x /= 5;
+x %= 6;
+x <<= 7;
+x >>= 8;
+x >>>= 9;
+x &= 10;
+x |= 11;
+x ^= 12;
+
+x++;
+x--;
+++x;
+--x;
+
+var a = x + 1;
+
+function f(v: number) { }
+f(x);
+
+if (x) { }
+
+x;
+(x);
+
+-x;
++x;
+
+x.toString();
+
+
+//// [letDeclarations-access.js]
+let x = 0;
+// No errors
+x = 1;
+x += 2;
+x -= 3;
+x *= 4;
+x /= 5;
+x %= 6;
+x <<= 7;
+x >>= 8;
+x >>>= 9;
+x &= 10;
+x |= 11;
+x ^= 12;
+x++;
+x--;
+++x;
+--x;
+var a = x + 1;
+function f(v) {
+}
+f(x);
+if (x) {
+}
+x;
+(x);
+-x;
++x;
+x.toString();
diff --git a/tests/baselines/reference/letDeclarations-access.types b/tests/baselines/reference/letDeclarations-access.types
new file mode 100644
index 0000000000000..f26d07ca5f8e8
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-access.types
@@ -0,0 +1,109 @@
+=== tests/cases/compiler/letDeclarations-access.ts ===
+
+let x = 0
+>x : number
+
+// No errors
+
+x = 1;
+>x = 1 : number
+>x : number
+
+x += 2;
+>x += 2 : number
+>x : number
+
+x -= 3;
+>x -= 3 : number
+>x : number
+
+x *= 4;
+>x *= 4 : number
+>x : number
+
+x /= 5;
+>x /= 5 : number
+>x : number
+
+x %= 6;
+>x %= 6 : number
+>x : number
+
+x <<= 7;
+>x <<= 7 : number
+>x : number
+
+x >>= 8;
+>x >>= 8 : number
+>x : number
+
+x >>>= 9;
+>x >>>= 9 : number
+>x : number
+
+x &= 10;
+>x &= 10 : number
+>x : number
+
+x |= 11;
+>x |= 11 : number
+>x : number
+
+x ^= 12;
+>x ^= 12 : number
+>x : number
+
+x++;
+>x++ : number
+>x : number
+
+x--;
+>x-- : number
+>x : number
+
+++x;
+>++x : number
+>x : number
+
+--x;
+>--x : number
+>x : number
+
+var a = x + 1;
+>a : number
+>x + 1 : number
+>x : number
+
+function f(v: number) { }
+>f : (v: number) => void
+>v : number
+
+f(x);
+>f(x) : void
+>f : (v: number) => void
+>x : number
+
+if (x) { }
+>x : number
+
+x;
+>x : number
+
+(x);
+>(x) : number
+>x : number
+
+-x;
+>-x : number
+>x : number
+
++x;
+>+x : number
+>x : number
+
+x.toString();
+>x.toString() : string
+>x.toString : (radix?: number) => string
+>x : number
+>toString : (radix?: number) => string
+
diff --git a/tests/baselines/reference/letDeclarations-es5.errors.txt b/tests/baselines/reference/letDeclarations-es5.errors.txt
new file mode 100644
index 0000000000000..be1a56a8b7fa5
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-es5.errors.txt
@@ -0,0 +1,40 @@
+tests/cases/compiler/letDeclarations-es5.ts(2,1): error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+tests/cases/compiler/letDeclarations-es5.ts(3,1): error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+tests/cases/compiler/letDeclarations-es5.ts(4,1): error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+tests/cases/compiler/letDeclarations-es5.ts(6,1): error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+tests/cases/compiler/letDeclarations-es5.ts(7,1): error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+tests/cases/compiler/letDeclarations-es5.ts(8,1): error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+tests/cases/compiler/letDeclarations-es5.ts(10,8): error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+tests/cases/compiler/letDeclarations-es5.ts(12,8): error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+
+
+==== tests/cases/compiler/letDeclarations-es5.ts (8 errors) ====
+    
+    let l1;
+    ~~~~~~~
+!!! error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+    let l2: number;
+    ~~~~~~~~~~~~~~~
+!!! error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+    let l3, l4, l5 :string, l6;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+    
+    let l7 = false;
+    ~~~~~~~~~~~~~~~
+!!! error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+    let l8: number = 23;
+    ~~~~~~~~~~~~~~~~~~~~
+!!! error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+    let l9 = 0, l10 :string = "", l11 = null;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+    
+    for(let l11 in {}) { }
+           ~~~~
+!!! error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+    
+    for(let l12 = 0; l12 < 9; l12++) { }
+           ~~~~~~~~
+!!! error TS1153: 'let' declarations are only available when targeting ECMAScript 6 and higher.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-invalidContexts.errors.txt b/tests/baselines/reference/letDeclarations-invalidContexts.errors.txt
new file mode 100644
index 0000000000000..ad0c0f741b5ce
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-invalidContexts.errors.txt
@@ -0,0 +1,66 @@
+tests/cases/compiler/letDeclarations-invalidContexts.ts(4,5): error TS1157: 'let' declarations can only be declared inside a block.
+tests/cases/compiler/letDeclarations-invalidContexts.ts(6,5): error TS1157: 'let' declarations can only be declared inside a block.
+tests/cases/compiler/letDeclarations-invalidContexts.ts(9,5): error TS1157: 'let' declarations can only be declared inside a block.
+tests/cases/compiler/letDeclarations-invalidContexts.ts(12,5): error TS1157: 'let' declarations can only be declared inside a block.
+tests/cases/compiler/letDeclarations-invalidContexts.ts(17,5): error TS1157: 'let' declarations can only be declared inside a block.
+tests/cases/compiler/letDeclarations-invalidContexts.ts(20,5): error TS1157: 'let' declarations can only be declared inside a block.
+tests/cases/compiler/letDeclarations-invalidContexts.ts(23,5): error TS1157: 'let' declarations can only be declared inside a block.
+tests/cases/compiler/letDeclarations-invalidContexts.ts(26,12): error TS1157: 'let' declarations can only be declared inside a block.
+tests/cases/compiler/letDeclarations-invalidContexts.ts(29,29): error TS1157: 'let' declarations can only be declared inside a block.
+tests/cases/compiler/letDeclarations-invalidContexts.ts(16,7): error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+
+
+==== tests/cases/compiler/letDeclarations-invalidContexts.ts (10 errors) ====
+    
+    // Errors, let must be defined inside a block
+    if (true) 
+        let l1 = 0;
+        ~~~~~~~~~~~
+!!! error TS1157: 'let' declarations can only be declared inside a block.
+    else 
+        let l2 = 0;
+        ~~~~~~~~~~~
+!!! error TS1157: 'let' declarations can only be declared inside a block.
+    
+    while (true) 
+        let l3 = 0;
+        ~~~~~~~~~~~
+!!! error TS1157: 'let' declarations can only be declared inside a block.
+    
+    do 
+        let l4 = 0;
+        ~~~~~~~~~~~
+!!! error TS1157: 'let' declarations can only be declared inside a block.
+    while (true);
+    
+    var obj;
+    with (obj) 
+          ~~~
+!!! error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+        let l5 = 0;
+        ~~~~~~~~~~~
+!!! error TS1157: 'let' declarations can only be declared inside a block.
+    
+    for (var i = 0; i < 10; i++)
+        let l6 = 0;
+        ~~~~~~~~~~~
+!!! error TS1157: 'let' declarations can only be declared inside a block.
+    
+    for (var i2 in {}) 
+        let l7 = 0;
+        ~~~~~~~~~~~
+!!! error TS1157: 'let' declarations can only be declared inside a block.
+    
+    if (true) 
+        label: let l8 = 0;
+               ~~~~~~~~~~~
+!!! error TS1157: 'let' declarations can only be declared inside a block.
+    
+    while (false)
+        label2: label3: label4: let l9 = 0;
+                                ~~~~~~~~~~~
+!!! error TS1157: 'let' declarations can only be declared inside a block.
+    
+    
+    
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-scopes-duplicates.errors.txt b/tests/baselines/reference/letDeclarations-scopes-duplicates.errors.txt
new file mode 100644
index 0000000000000..b3b620a4c9ee8
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes-duplicates.errors.txt
@@ -0,0 +1,152 @@
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(3,5): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(4,5): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(6,5): error TS2451: Cannot redeclare block-scoped variable 'var2'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(7,7): error TS2451: Cannot redeclare block-scoped variable 'var2'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(9,7): error TS2451: Cannot redeclare block-scoped variable 'var3'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(10,5): error TS2451: Cannot redeclare block-scoped variable 'var3'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(12,7): error TS2451: Cannot redeclare block-scoped variable 'var4'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(13,7): error TS2451: Cannot redeclare block-scoped variable 'var4'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(15,5): error TS2300: Duplicate identifier 'var5'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(16,5): error TS2300: Duplicate identifier 'var5'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(18,5): error TS2451: Cannot redeclare block-scoped variable 'var6'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(19,5): error TS2451: Cannot redeclare block-scoped variable 'var6'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(22,9): error TS2451: Cannot redeclare block-scoped variable 'var7'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(23,9): error TS2451: Cannot redeclare block-scoped variable 'var7'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(25,13): error TS2451: Cannot redeclare block-scoped variable 'var8'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(26,15): error TS2451: Cannot redeclare block-scoped variable 'var8'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(32,13): error TS2451: Cannot redeclare block-scoped variable 'var9'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(33,13): error TS2451: Cannot redeclare block-scoped variable 'var9'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(37,11): error TS2451: Cannot redeclare block-scoped variable 'var10'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(38,11): error TS2451: Cannot redeclare block-scoped variable 'var10'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(41,9): error TS2451: Cannot redeclare block-scoped variable 'var11'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(42,9): error TS2451: Cannot redeclare block-scoped variable 'var11'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(46,9): error TS2451: Cannot redeclare block-scoped variable 'var12'.
+tests/cases/compiler/letDeclarations-scopes-duplicates.ts(47,9): error TS2451: Cannot redeclare block-scoped variable 'var12'.
+
+
+==== tests/cases/compiler/letDeclarations-scopes-duplicates.ts (24 errors) ====
+    
+    // Errors: redeclaration
+    let var1 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
+    let var1 = 0; // error
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
+    
+    let var2 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var2'.
+    const var2 = 0;
+          ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var2'.
+    
+    const var3 = 0;
+          ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var3'.
+    let var3 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var3'.
+    
+    const var4 = 0;
+          ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var4'.
+    const var4 = 0;
+          ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var4'.
+    
+    var var5 = 0;
+        ~~~~
+!!! error TS2300: Duplicate identifier 'var5'.
+    let var5 = 0;
+        ~~~~
+!!! error TS2300: Duplicate identifier 'var5'.
+    
+    let var6 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var6'.
+    var var6 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var6'.
+    
+    {
+        let var7 = 0;
+            ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var7'.
+        let var7 = 0;
+            ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var7'.
+        {
+            let var8 = 0;
+                ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var8'.
+            const var8 = 0;
+                  ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var8'.
+        }
+    }
+    
+    switch (0) {
+        default:
+            let var9 = 0;
+                ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var9'.
+            let var9 = 0;
+                ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var9'.
+    }
+    
+    try {
+        const var10 = 0;
+              ~~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var10'.
+        const var10 = 0;
+              ~~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var10'.
+    }
+    catch (e) {
+        let var11 = 0;
+            ~~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var11'.
+        let var11 = 0;
+            ~~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var11'.
+    }
+    
+    function F1() {
+        let var12;
+            ~~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var12'.
+        let var12;
+            ~~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var12'.
+    }
+    
+    // OK
+    var var20 = 0;
+    
+    var var20 = 0
+    {
+        let var20 = 0;
+        {
+            let var20 = 0;
+        }
+    }
+    
+    switch (0) {
+        default:
+            let var20 = 0;
+    }
+    
+    try {
+        let var20 = 0;
+    }
+    catch (e) {
+        let var20 = 0;
+    }
+    
+    function F() {
+        let var20;
+    }
+    
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-scopes-duplicates2.errors.txt b/tests/baselines/reference/letDeclarations-scopes-duplicates2.errors.txt
new file mode 100644
index 0000000000000..72b8b5609b695
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes-duplicates2.errors.txt
@@ -0,0 +1,14 @@
+tests/cases/compiler/file1.ts(2,5): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+tests/cases/compiler/file2.ts(1,5): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+
+
+==== tests/cases/compiler/file1.ts (1 errors) ====
+    
+    let var1 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
+    
+==== tests/cases/compiler/file2.ts (1 errors) ====
+    let var1 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-scopes-duplicates3.errors.txt b/tests/baselines/reference/letDeclarations-scopes-duplicates3.errors.txt
new file mode 100644
index 0000000000000..6ed2fb66195ba
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes-duplicates3.errors.txt
@@ -0,0 +1,14 @@
+tests/cases/compiler/file1.ts(2,5): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+tests/cases/compiler/file2.ts(1,7): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+
+
+==== tests/cases/compiler/file1.ts (1 errors) ====
+    
+    let var1 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
+    
+==== tests/cases/compiler/file2.ts (1 errors) ====
+    const var1 = 0;
+          ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-scopes-duplicates4.errors.txt b/tests/baselines/reference/letDeclarations-scopes-duplicates4.errors.txt
new file mode 100644
index 0000000000000..ec87809b0cda5
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes-duplicates4.errors.txt
@@ -0,0 +1,14 @@
+tests/cases/compiler/file1.ts(2,7): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+tests/cases/compiler/file2.ts(1,5): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+
+
+==== tests/cases/compiler/file1.ts (1 errors) ====
+    
+    const var1 = 0;
+          ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
+    
+==== tests/cases/compiler/file2.ts (1 errors) ====
+    let var1 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-scopes-duplicates5.errors.txt b/tests/baselines/reference/letDeclarations-scopes-duplicates5.errors.txt
new file mode 100644
index 0000000000000..ce3a9da598a4a
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes-duplicates5.errors.txt
@@ -0,0 +1,14 @@
+tests/cases/compiler/file1.ts(2,7): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+tests/cases/compiler/file2.ts(1,7): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+
+
+==== tests/cases/compiler/file1.ts (1 errors) ====
+    
+    const var1 = 0;
+          ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
+    
+==== tests/cases/compiler/file2.ts (1 errors) ====
+    const var1 = 0;
+          ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-scopes-duplicates6.errors.txt b/tests/baselines/reference/letDeclarations-scopes-duplicates6.errors.txt
new file mode 100644
index 0000000000000..d09eda28075d8
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes-duplicates6.errors.txt
@@ -0,0 +1,14 @@
+tests/cases/compiler/file1.ts(2,5): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+tests/cases/compiler/file2.ts(1,5): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+
+
+==== tests/cases/compiler/file1.ts (1 errors) ====
+    
+    var var1 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
+    
+==== tests/cases/compiler/file2.ts (1 errors) ====
+    let var1 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-scopes-duplicates7.errors.txt b/tests/baselines/reference/letDeclarations-scopes-duplicates7.errors.txt
new file mode 100644
index 0000000000000..dad85f9f81946
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes-duplicates7.errors.txt
@@ -0,0 +1,14 @@
+tests/cases/compiler/file1.ts(2,5): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+tests/cases/compiler/file2.ts(1,5): error TS2451: Cannot redeclare block-scoped variable 'var1'.
+
+
+==== tests/cases/compiler/file1.ts (1 errors) ====
+    
+    let var1 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
+    
+==== tests/cases/compiler/file2.ts (1 errors) ====
+    var var1 = 0;
+        ~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'var1'.
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-scopes.errors.txt b/tests/baselines/reference/letDeclarations-scopes.errors.txt
new file mode 100644
index 0000000000000..5c89ea98049a6
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes.errors.txt
@@ -0,0 +1,163 @@
+tests/cases/compiler/letDeclarations-scopes.ts(28,7): error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+
+
+==== tests/cases/compiler/letDeclarations-scopes.ts (1 errors) ====
+    
+    // global
+    let l = "string";
+    
+    var n: number;
+    
+    // Control flow statements with blocks
+    if (true) {
+        let l = 0;
+        n = l;
+    }
+    else {
+        let l = 0;
+        n = l;
+    }
+    
+    while (true) {
+        let l = 0;
+        n = l;
+    }
+    
+    do {
+       let l = 0;
+        n = l;
+    } while (true);
+    
+    var obj;
+    with (obj) {
+          ~~~
+!!! error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+        let l = 0;
+        n = l;
+    }
+    
+    for (var i = 0; i < 10; i++) {
+        let l = 0;
+        n = l;
+    }
+    
+    for (var i2 in {}) {
+        let l = 0;
+        n = l;
+    }
+    
+    if (true) {
+        label: let l = 0;
+        n = l;
+    }
+    
+    while (false) {
+        label2: label3: label4: let l = 0;
+        n = l;
+    }
+    
+    for (let l = 0; n = l; l++) {
+        let l = true;
+        var b3: boolean = l;
+    }
+    
+    for (let l in {}) {
+    
+    }
+    
+    // Try/catch/finally
+    try {
+        let l = 0;
+        n = l;
+    }
+    catch (e) {
+        let l = 0;
+        n = l;
+    }
+    finally {
+        let l = 0;
+        n = l;
+    }
+    
+    // Switch
+    switch (0) {
+        case 0:
+            let l = 0;
+            n = l;
+            break;
+    }
+    
+    // blocks
+    {
+        let l = 0;
+        n = l;
+        {
+            let l = false;
+            var b: boolean = l;
+        }
+    }
+    
+    // functions
+    function F() {
+        let l = 0;
+        n = l;
+    }
+    
+    var F2 = () => {
+        let l = 0;
+        n = l;
+    };
+    
+    var F3 = function () {
+        let l = 0;
+        n = l;
+    };
+    
+    // modules
+    module m {
+        let l = 0;
+        n = l;
+    
+        {
+           let l = false;
+           var b2: boolean = l;
+        }
+    
+        lable: let l2 = 0;
+    }
+    
+    // methods
+    class C {
+        constructor() {
+            let l = 0;
+            n = l;
+        }
+    
+        method() {
+            let l = 0;
+            n = l;
+        }
+    
+        get v() {
+            let l = 0;
+            n = l;
+            return n;
+        }
+    
+        set v(value) {
+            let l = 0;
+            n = l;
+        }
+    }
+    
+    // object literals
+    var o = {
+        f() {
+            let l = 0;
+            n = l;
+        },
+        f2: () => {
+            let l = 0;
+            n = l;
+        }
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-scopes.js b/tests/baselines/reference/letDeclarations-scopes.js
new file mode 100644
index 0000000000000..fb16a03f569f8
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes.js
@@ -0,0 +1,293 @@
+//// [letDeclarations-scopes.ts]
+
+// global
+let l = "string";
+
+var n: number;
+
+// Control flow statements with blocks
+if (true) {
+    let l = 0;
+    n = l;
+}
+else {
+    let l = 0;
+    n = l;
+}
+
+while (true) {
+    let l = 0;
+    n = l;
+}
+
+do {
+   let l = 0;
+    n = l;
+} while (true);
+
+var obj;
+with (obj) {
+    let l = 0;
+    n = l;
+}
+
+for (var i = 0; i < 10; i++) {
+    let l = 0;
+    n = l;
+}
+
+for (var i2 in {}) {
+    let l = 0;
+    n = l;
+}
+
+if (true) {
+    label: let l = 0;
+    n = l;
+}
+
+while (false) {
+    label2: label3: label4: let l = 0;
+    n = l;
+}
+
+for (let l = 0; n = l; l++) {
+    let l = true;
+    var b3: boolean = l;
+}
+
+for (let l in {}) {
+
+}
+
+// Try/catch/finally
+try {
+    let l = 0;
+    n = l;
+}
+catch (e) {
+    let l = 0;
+    n = l;
+}
+finally {
+    let l = 0;
+    n = l;
+}
+
+// Switch
+switch (0) {
+    case 0:
+        let l = 0;
+        n = l;
+        break;
+}
+
+// blocks
+{
+    let l = 0;
+    n = l;
+    {
+        let l = false;
+        var b: boolean = l;
+    }
+}
+
+// functions
+function F() {
+    let l = 0;
+    n = l;
+}
+
+var F2 = () => {
+    let l = 0;
+    n = l;
+};
+
+var F3 = function () {
+    let l = 0;
+    n = l;
+};
+
+// modules
+module m {
+    let l = 0;
+    n = l;
+
+    {
+       let l = false;
+       var b2: boolean = l;
+    }
+
+    lable: let l2 = 0;
+}
+
+// methods
+class C {
+    constructor() {
+        let l = 0;
+        n = l;
+    }
+
+    method() {
+        let l = 0;
+        n = l;
+    }
+
+    get v() {
+        let l = 0;
+        n = l;
+        return n;
+    }
+
+    set v(value) {
+        let l = 0;
+        n = l;
+    }
+}
+
+// object literals
+var o = {
+    f() {
+        let l = 0;
+        n = l;
+    },
+    f2: () => {
+        let l = 0;
+        n = l;
+    }
+}
+
+//// [letDeclarations-scopes.js]
+// global
+let l = "string";
+var n;
+// Control flow statements with blocks
+if (true) {
+    let l = 0;
+    n = l;
+}
+else {
+    let l = 0;
+    n = l;
+}
+while (true) {
+    let l = 0;
+    n = l;
+}
+do {
+    let l = 0;
+    n = l;
+} while (true);
+var obj;
+with (obj) {
+    let l = 0;
+    n = l;
+}
+for (var i = 0; i < 10; i++) {
+    let l = 0;
+    n = l;
+}
+for (var i2 in {}) {
+    let l = 0;
+    n = l;
+}
+if (true) {
+    label: let l = 0;
+    n = l;
+}
+while (false) {
+    label2: label3: label4: let l = 0;
+    n = l;
+}
+for (let l = 0; n = l; l++) {
+    let l = true;
+    var b3 = l;
+}
+for (let l in {}) {
+}
+try {
+    let l = 0;
+    n = l;
+}
+catch (e) {
+    let l = 0;
+    n = l;
+}
+finally {
+    let l = 0;
+    n = l;
+}
+switch (0) {
+    case 0:
+        let l = 0;
+        n = l;
+        break;
+}
+{
+    let l = 0;
+    n = l;
+    {
+        let l = false;
+        var b = l;
+    }
+}
+// functions
+function F() {
+    let l = 0;
+    n = l;
+}
+var F2 = function () {
+    let l = 0;
+    n = l;
+};
+var F3 = function () {
+    let l = 0;
+    n = l;
+};
+// modules
+var m;
+(function (m) {
+    let l = 0;
+    n = l;
+    {
+        let l = false;
+        var b2 = l;
+    }
+    lable: let l2 = 0;
+})(m || (m = {}));
+// methods
+var C = (function () {
+    function C() {
+        let l = 0;
+        n = l;
+    }
+    C.prototype.method = function () {
+        let l = 0;
+        n = l;
+    };
+    Object.defineProperty(C.prototype, "v", {
+        get: function () {
+            let l = 0;
+            n = l;
+            return n;
+        },
+        set: function (value) {
+            let l = 0;
+            n = l;
+        },
+        enumerable: true,
+        configurable: true
+    });
+    return C;
+})();
+// object literals
+var o = {
+    f: function () {
+        let l = 0;
+        n = l;
+    },
+    f2: function () {
+        let l = 0;
+        n = l;
+    }
+};
diff --git a/tests/baselines/reference/letDeclarations-scopes2.errors.txt b/tests/baselines/reference/letDeclarations-scopes2.errors.txt
new file mode 100644
index 0000000000000..a786db1104b79
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes2.errors.txt
@@ -0,0 +1,42 @@
+tests/cases/compiler/letDeclarations-scopes2.ts(9,5): error TS2304: Cannot find name 'local2'.
+tests/cases/compiler/letDeclarations-scopes2.ts(21,5): error TS2304: Cannot find name 'local2'.
+tests/cases/compiler/letDeclarations-scopes2.ts(24,1): error TS2304: Cannot find name 'local'.
+tests/cases/compiler/letDeclarations-scopes2.ts(26,1): error TS2304: Cannot find name 'local2'.
+
+
+==== tests/cases/compiler/letDeclarations-scopes2.ts (4 errors) ====
+    
+    let global = 0;
+    
+    { 
+        let local = 0;
+    
+        local;  // OK
+        global; // OK
+        local2; // Error
+        ~~~~~~
+!!! error TS2304: Cannot find name 'local2'.
+    
+        {
+            let local2 = 0;
+    
+            local;  // OK
+            global; // OK
+            local2; // OK
+        } 
+    
+        local;  // OK
+        global; // OK
+        local2; // Error
+        ~~~~~~
+!!! error TS2304: Cannot find name 'local2'.
+    }
+    
+    local;  // Error
+    ~~~~~
+!!! error TS2304: Cannot find name 'local'.
+    global; // OK
+    local2; // Error
+    ~~~~~~
+!!! error TS2304: Cannot find name 'local2'.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-scopes2.js b/tests/baselines/reference/letDeclarations-scopes2.js
new file mode 100644
index 0000000000000..98d0e791832e0
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-scopes2.js
@@ -0,0 +1,49 @@
+//// [letDeclarations-scopes2.ts]
+
+let global = 0;
+
+{ 
+    let local = 0;
+
+    local;  // OK
+    global; // OK
+    local2; // Error
+
+    {
+        let local2 = 0;
+
+        local;  // OK
+        global; // OK
+        local2; // OK
+    } 
+
+    local;  // OK
+    global; // OK
+    local2; // Error
+}
+
+local;  // Error
+global; // OK
+local2; // Error
+
+
+//// [letDeclarations-scopes2.js]
+let global = 0;
+{
+    let local = 0;
+    local; // OK
+    global; // OK
+    local2; // Error
+    {
+        let local2 = 0;
+        local; // OK
+        global; // OK
+        local2; // OK
+    }
+    local; // OK
+    global; // OK
+    local2; // Error
+}
+local; // Error
+global; // OK
+local2; // Error
diff --git a/tests/baselines/reference/letDeclarations-useBeforeDefinition.errors.txt b/tests/baselines/reference/letDeclarations-useBeforeDefinition.errors.txt
new file mode 100644
index 0000000000000..74c354f4ff26f
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-useBeforeDefinition.errors.txt
@@ -0,0 +1,21 @@
+tests/cases/compiler/letDeclarations-useBeforeDefinition.ts(3,5): error TS2448: Block-scoped variable 'l1' used before its declaration.
+tests/cases/compiler/letDeclarations-useBeforeDefinition.ts(9,5): error TS2448: Block-scoped variable 'v1' used before its declaration.
+
+
+==== tests/cases/compiler/letDeclarations-useBeforeDefinition.ts (2 errors) ====
+    
+    {
+        l1;
+        ~~
+!!! error TS2448: Block-scoped variable 'l1' used before its declaration.
+        let l1;
+    }
+    
+    var v1;
+    {
+        v1;
+        ~~
+!!! error TS2448: Block-scoped variable 'v1' used before its declaration.
+        let v1 = 0;
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-useBeforeDefinition2.errors.txt b/tests/baselines/reference/letDeclarations-useBeforeDefinition2.errors.txt
new file mode 100644
index 0000000000000..5b8633312d9a9
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-useBeforeDefinition2.errors.txt
@@ -0,0 +1,11 @@
+tests/cases/compiler/file1.ts(2,1): error TS2448: Block-scoped variable 'l' used before its declaration.
+
+
+==== tests/cases/compiler/file1.ts (1 errors) ====
+    
+    l;
+    ~
+!!! error TS2448: Block-scoped variable 'l' used before its declaration.
+    
+==== tests/cases/compiler/file2.ts (0 errors) ====
+    const l = 0;
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-validContexts.errors.txt b/tests/baselines/reference/letDeclarations-validContexts.errors.txt
new file mode 100644
index 0000000000000..3f3b7a2634f09
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-validContexts.errors.txt
@@ -0,0 +1,149 @@
+tests/cases/compiler/letDeclarations-validContexts.ts(20,7): error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+
+
+==== tests/cases/compiler/letDeclarations-validContexts.ts (1 errors) ====
+    
+    
+    // Control flow statements with blocks
+    if (true) { 
+        let l1 = 0;
+    }
+    else { 
+        let l2 = 0;
+    }
+    
+    while (true) { 
+        let l3 = 0;
+    }
+    
+    do { 
+        let l4 = 0;
+    } while (true);
+    
+    var obj;
+    with (obj) {
+          ~~~
+!!! error TS2410: All symbols within a 'with' block will be resolved to 'any'.
+        let l5 = 0;
+    }
+    
+    for (var i = 0; i < 10; i++) {
+        let l6 = 0;
+    }
+    
+    for (var i2 in {}) {
+        let l7 = 0;
+    }
+    
+    if (true) {
+        label: let l8 = 0;
+    }
+    
+    while (false) {
+        label2: label3: label4: let l9 = 0;
+    }
+    
+    // Try/catch/finally
+    try {
+        let l10 = 0;
+    }
+    catch (e) {
+        let l11 = 0;
+    }
+    finally {
+        let l12 = 0;
+    }
+    
+    // Switch
+    switch (0) {
+        case 0:
+            let l13 = 0;
+            break;
+        default:
+            let l14 = 0;
+            break;
+    }
+    
+    // blocks
+    {
+        let l15 = 0;
+        {
+            let l16 = 0
+            label17: let l17 = 0;
+        }
+    }
+    
+    // global
+    let l18 = 0;
+    
+    // functions
+    function F() {
+        let l19 = 0;
+    }
+    
+    var F2 = () => {
+        let l20 = 0;
+    };
+    
+    var F3 = function () {
+        let l21 = 0;
+    };
+    
+    // modules
+    module m {
+        let l22 = 0;
+    
+        {
+              let l23 = 0;
+        }
+    }
+    
+    // methods
+    class C {
+        constructor() {
+            let l24 = 0;
+        }
+    
+        method() {
+            let l25 = 0;
+        }
+    
+        get v() {
+            let l26 = 0;
+            return l26; 
+        }
+    
+        set v(value) {
+            let l27 = value;
+        }
+    }
+    
+    // object literals
+    var o = {
+        f() {
+            let l28 = 0;
+        },
+        f2: () => {
+            let l29 = 0;
+        }
+    }
+    
+    // labels
+    label: let l30 = 0;
+    {
+        label2: let l31 = 0;
+    }
+    
+    function f3() {
+        label: let l32 = 0;
+        {
+            label2: let l33 = 0;
+        }
+    }
+    
+    module m3 {
+        label: let l34 = 0;
+        {
+            label2: let l35 = 0;
+        }
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/letDeclarations-validContexts.js b/tests/baselines/reference/letDeclarations-validContexts.js
new file mode 100644
index 0000000000000..13eaafb07120d
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations-validContexts.js
@@ -0,0 +1,266 @@
+//// [letDeclarations-validContexts.ts]
+
+
+// Control flow statements with blocks
+if (true) { 
+    let l1 = 0;
+}
+else { 
+    let l2 = 0;
+}
+
+while (true) { 
+    let l3 = 0;
+}
+
+do { 
+    let l4 = 0;
+} while (true);
+
+var obj;
+with (obj) {
+    let l5 = 0;
+}
+
+for (var i = 0; i < 10; i++) {
+    let l6 = 0;
+}
+
+for (var i2 in {}) {
+    let l7 = 0;
+}
+
+if (true) {
+    label: let l8 = 0;
+}
+
+while (false) {
+    label2: label3: label4: let l9 = 0;
+}
+
+// Try/catch/finally
+try {
+    let l10 = 0;
+}
+catch (e) {
+    let l11 = 0;
+}
+finally {
+    let l12 = 0;
+}
+
+// Switch
+switch (0) {
+    case 0:
+        let l13 = 0;
+        break;
+    default:
+        let l14 = 0;
+        break;
+}
+
+// blocks
+{
+    let l15 = 0;
+    {
+        let l16 = 0
+        label17: let l17 = 0;
+    }
+}
+
+// global
+let l18 = 0;
+
+// functions
+function F() {
+    let l19 = 0;
+}
+
+var F2 = () => {
+    let l20 = 0;
+};
+
+var F3 = function () {
+    let l21 = 0;
+};
+
+// modules
+module m {
+    let l22 = 0;
+
+    {
+          let l23 = 0;
+    }
+}
+
+// methods
+class C {
+    constructor() {
+        let l24 = 0;
+    }
+
+    method() {
+        let l25 = 0;
+    }
+
+    get v() {
+        let l26 = 0;
+        return l26; 
+    }
+
+    set v(value) {
+        let l27 = value;
+    }
+}
+
+// object literals
+var o = {
+    f() {
+        let l28 = 0;
+    },
+    f2: () => {
+        let l29 = 0;
+    }
+}
+
+// labels
+label: let l30 = 0;
+{
+    label2: let l31 = 0;
+}
+
+function f3() {
+    label: let l32 = 0;
+    {
+        label2: let l33 = 0;
+    }
+}
+
+module m3 {
+    label: let l34 = 0;
+    {
+        label2: let l35 = 0;
+    }
+}
+
+//// [letDeclarations-validContexts.js]
+// Control flow statements with blocks
+if (true) {
+    let l1 = 0;
+}
+else {
+    let l2 = 0;
+}
+while (true) {
+    let l3 = 0;
+}
+do {
+    let l4 = 0;
+} while (true);
+var obj;
+with (obj) {
+    let l5 = 0;
+}
+for (var i = 0; i < 10; i++) {
+    let l6 = 0;
+}
+for (var i2 in {}) {
+    let l7 = 0;
+}
+if (true) {
+    label: let l8 = 0;
+}
+while (false) {
+    label2: label3: label4: let l9 = 0;
+}
+try {
+    let l10 = 0;
+}
+catch (e) {
+    let l11 = 0;
+}
+finally {
+    let l12 = 0;
+}
+switch (0) {
+    case 0:
+        let l13 = 0;
+        break;
+    default:
+        let l14 = 0;
+        break;
+}
+{
+    let l15 = 0;
+    {
+        let l16 = 0;
+        label17: let l17 = 0;
+    }
+}
+// global
+let l18 = 0;
+// functions
+function F() {
+    let l19 = 0;
+}
+var F2 = function () {
+    let l20 = 0;
+};
+var F3 = function () {
+    let l21 = 0;
+};
+// modules
+var m;
+(function (m) {
+    let l22 = 0;
+    {
+        let l23 = 0;
+    }
+})(m || (m = {}));
+// methods
+var C = (function () {
+    function C() {
+        let l24 = 0;
+    }
+    C.prototype.method = function () {
+        let l25 = 0;
+    };
+    Object.defineProperty(C.prototype, "v", {
+        get: function () {
+            let l26 = 0;
+            return l26;
+        },
+        set: function (value) {
+            let l27 = value;
+        },
+        enumerable: true,
+        configurable: true
+    });
+    return C;
+})();
+// object literals
+var o = {
+    f: function () {
+        let l28 = 0;
+    },
+    f2: function () {
+        let l29 = 0;
+    }
+};
+label: let l30 = 0;
+{
+    label2: let l31 = 0;
+}
+function f3() {
+    label: let l32 = 0;
+    {
+        label2: let l33 = 0;
+    }
+}
+var m3;
+(function (m3) {
+    label: let l34 = 0;
+    {
+        label2: let l35 = 0;
+    }
+})(m3 || (m3 = {}));
diff --git a/tests/baselines/reference/letDeclarations.js b/tests/baselines/reference/letDeclarations.js
new file mode 100644
index 0000000000000..bc186b732f559
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations.js
@@ -0,0 +1,35 @@
+//// [letDeclarations.ts]
+
+let l1;
+let l2: number;
+let l3, l4, l5 :string, l6;
+
+let l7 = false;
+let l8: number = 23;
+let l9 = 0, l10 :string = "", l11 = null;
+
+for(let l11 in {}) { }
+
+for(let l12 = 0; l12 < 9; l12++) { }
+
+
+//// [letDeclarations.js]
+let l1;
+let l2;
+let l3, l4, l5, l6;
+let l7 = false;
+let l8 = 23;
+let l9 = 0, l10 = "", l11 = null;
+for (let l11 in {}) {
+}
+for (let l12 = 0; l12 < 9; l12++) {
+}
+
+
+//// [letDeclarations.d.ts]
+declare let l1: any;
+declare let l2: number;
+declare let l3: any, l4: any, l5: string, l6: any;
+declare let l7: boolean;
+declare let l8: number;
+declare let l9: number, l10: string, l11: any;
diff --git a/tests/baselines/reference/letDeclarations.types b/tests/baselines/reference/letDeclarations.types
new file mode 100644
index 0000000000000..aa47a7f000645
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations.types
@@ -0,0 +1,36 @@
+=== tests/cases/compiler/letDeclarations.ts ===
+
+let l1;
+>l1 : any
+
+let l2: number;
+>l2 : number
+
+let l3, l4, l5 :string, l6;
+>l3 : any
+>l4 : any
+>l5 : string
+>l6 : any
+
+let l7 = false;
+>l7 : boolean
+
+let l8: number = 23;
+>l8 : number
+
+let l9 = 0, l10 :string = "", l11 = null;
+>l9 : number
+>l10 : string
+>l11 : any
+
+for(let l11 in {}) { }
+>l11 : any
+>{} : {}
+
+for(let l12 = 0; l12 < 9; l12++) { }
+>l12 : number
+>l12 < 9 : boolean
+>l12 : number
+>l12++ : number
+>l12 : number
+
diff --git a/tests/baselines/reference/letDeclarations2.js b/tests/baselines/reference/letDeclarations2.js
new file mode 100644
index 0000000000000..8a6f039f2ca93
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations2.js
@@ -0,0 +1,19 @@
+//// [letDeclarations2.ts]
+
+module M {
+    let l1 = "s";
+    export let l2 = 0;
+}
+
+//// [letDeclarations2.js]
+var M;
+(function (M) {
+    let l1 = "s";
+    M.l2 = 0;
+})(M || (M = {}));
+
+
+//// [letDeclarations2.d.ts]
+declare module M {
+    let l2: number;
+}
diff --git a/tests/baselines/reference/letDeclarations2.types b/tests/baselines/reference/letDeclarations2.types
new file mode 100644
index 0000000000000..2fa08b6d9400b
--- /dev/null
+++ b/tests/baselines/reference/letDeclarations2.types
@@ -0,0 +1,11 @@
+=== tests/cases/compiler/letDeclarations2.ts ===
+
+module M {
+>M : typeof M
+
+    let l1 = "s";
+>l1 : string
+
+    export let l2 = 0;
+>l2 : number
+}
diff --git a/tests/baselines/reference/parserEnum5.errors.txt b/tests/baselines/reference/parserEnum5.errors.txt
index 40c2c933955a6..b98fdfbfba503 100644
--- a/tests/baselines/reference/parserEnum5.errors.txt
+++ b/tests/baselines/reference/parserEnum5.errors.txt
@@ -1,9 +1,9 @@
 tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts(2,12): error TS1005: ',' expected.
 tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts(3,15): error TS1005: ',' expected.
 tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts(3,24): error TS1005: ',' expected.
-tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts(2,14): error TS1151: An enum member cannot have a numeric name.
-tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts(3,17): error TS1151: An enum member cannot have a numeric name.
-tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts(3,26): error TS1151: An enum member cannot have a numeric name.
+tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts(2,14): error TS2452: An enum member cannot have a numeric name.
+tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts(3,17): error TS2452: An enum member cannot have a numeric name.
+tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts(3,26): error TS2452: An enum member cannot have a numeric name.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts (6 errors) ====
@@ -12,13 +12,13 @@ tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum5.ts(3,26)
                ~
 !!! error TS1005: ',' expected.
                  ~
-!!! error TS1151: An enum member cannot have a numeric name.
+!!! error TS2452: An enum member cannot have a numeric name.
     enum E1 { a, b: 1, c, d: 2 = 3 }
                   ~
 !!! error TS1005: ',' expected.
                            ~
 !!! error TS1005: ',' expected.
                     ~
-!!! error TS1151: An enum member cannot have a numeric name.
+!!! error TS2452: An enum member cannot have a numeric name.
                              ~
-!!! error TS1151: An enum member cannot have a numeric name.
\ No newline at end of file
+!!! error TS2452: An enum member cannot have a numeric name.
\ No newline at end of file
diff --git a/tests/baselines/reference/parserEnum7.errors.txt b/tests/baselines/reference/parserEnum7.errors.txt
index a4a2326546a05..1a7f26df8db9c 100644
--- a/tests/baselines/reference/parserEnum7.errors.txt
+++ b/tests/baselines/reference/parserEnum7.errors.txt
@@ -1,15 +1,15 @@
-tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum7.ts(2,3): error TS1151: An enum member cannot have a numeric name.
-tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum7.ts(2,6): error TS1151: An enum member cannot have a numeric name.
-tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum7.ts(2,9): error TS1151: An enum member cannot have a numeric name.
+tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum7.ts(2,3): error TS2452: An enum member cannot have a numeric name.
+tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum7.ts(2,6): error TS2452: An enum member cannot have a numeric name.
+tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum7.ts(2,9): error TS2452: An enum member cannot have a numeric name.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/EnumDeclarations/parserEnum7.ts (3 errors) ====
     enum E {
       1, 2, 3
       ~
-!!! error TS1151: An enum member cannot have a numeric name.
+!!! error TS2452: An enum member cannot have a numeric name.
          ~
-!!! error TS1151: An enum member cannot have a numeric name.
+!!! error TS2452: An enum member cannot have a numeric name.
             ~
-!!! error TS1151: An enum member cannot have a numeric name.
+!!! error TS2452: An enum member cannot have a numeric name.
     }
\ No newline at end of file
diff --git a/tests/baselines/reference/parserOptionalTypeMembers1.errors.txt b/tests/baselines/reference/parserOptionalTypeMembers1.errors.txt
deleted file mode 100644
index 0279ad37777ef..0000000000000
--- a/tests/baselines/reference/parserOptionalTypeMembers1.errors.txt
+++ /dev/null
@@ -1,23 +0,0 @@
-tests/cases/conformance/parser/ecmascript5/parserOptionalTypeMembers1.ts(2,5): error TS2300: Duplicate identifier 'configurable'.
-tests/cases/conformance/parser/ecmascript5/parserOptionalTypeMembers1.ts(3,5): error TS2300: Duplicate identifier 'enumerable'.
-tests/cases/conformance/parser/ecmascript5/parserOptionalTypeMembers1.ts(4,5): error TS2300: Duplicate identifier 'value'.
-tests/cases/conformance/parser/ecmascript5/parserOptionalTypeMembers1.ts(5,5): error TS2300: Duplicate identifier 'writable'.
-
-
-==== tests/cases/conformance/parser/ecmascript5/parserOptionalTypeMembers1.ts (4 errors) ====
-    interface PropertyDescriptor {
-        configurable?: boolean;
-        ~~~~~~~~~~~~
-!!! error TS2300: Duplicate identifier 'configurable'.
-        enumerable?: boolean;
-        ~~~~~~~~~~
-!!! error TS2300: Duplicate identifier 'enumerable'.
-        value?: any;
-        ~~~~~
-!!! error TS2300: Duplicate identifier 'value'.
-        writable?: boolean;
-        ~~~~~~~~
-!!! error TS2300: Duplicate identifier 'writable'.
-        get?(): any;
-        set?(v: any): void;
-    }
\ No newline at end of file
diff --git a/tests/baselines/reference/parserOptionalTypeMembers1.js b/tests/baselines/reference/parserOptionalTypeMembers1.js
index 5dfb0adfe8260..757887e540966 100644
--- a/tests/baselines/reference/parserOptionalTypeMembers1.js
+++ b/tests/baselines/reference/parserOptionalTypeMembers1.js
@@ -1,5 +1,5 @@
 //// [parserOptionalTypeMembers1.ts]
-interface PropertyDescriptor {
+interface PropertyDescriptor2 {
     configurable?: boolean;
     enumerable?: boolean;
     value?: any;
diff --git a/tests/baselines/reference/parserOptionalTypeMembers1.types b/tests/baselines/reference/parserOptionalTypeMembers1.types
new file mode 100644
index 0000000000000..7ede18a1d9246
--- /dev/null
+++ b/tests/baselines/reference/parserOptionalTypeMembers1.types
@@ -0,0 +1,23 @@
+=== tests/cases/conformance/parser/ecmascript5/parserOptionalTypeMembers1.ts ===
+interface PropertyDescriptor2 {
+>PropertyDescriptor2 : PropertyDescriptor2
+
+    configurable?: boolean;
+>configurable : boolean
+
+    enumerable?: boolean;
+>enumerable : boolean
+
+    value?: any;
+>value : any
+
+    writable?: boolean;
+>writable : boolean
+
+    get?(): any;
+>get : () => any
+
+    set?(v: any): void;
+>set : (v: any) => void
+>v : any
+}
diff --git a/tests/baselines/reference/project/declareVariableCollision/amd/declareVariableCollision.errors.txt b/tests/baselines/reference/project/declareVariableCollision/amd/declareVariableCollision.errors.txt
index 5dc0a63d7eb11..64ec399fabf71 100644
--- a/tests/baselines/reference/project/declareVariableCollision/amd/declareVariableCollision.errors.txt
+++ b/tests/baselines/reference/project/declareVariableCollision/amd/declareVariableCollision.errors.txt
@@ -1,3 +1,4 @@
+in1.d.ts(1,8): error TS2300: Duplicate identifier 'a'.
 in2.d.ts(1,8): error TS2300: Duplicate identifier 'a'.
 
 
@@ -14,8 +15,10 @@ in2.d.ts(1,8): error TS2300: Duplicate identifier 'a'.
             class MyClass{ }
         }
     }
-==== in1.d.ts (0 errors) ====
+==== in1.d.ts (1 errors) ====
     import a = A;
+           ~
+!!! error TS2300: Duplicate identifier 'a'.
 ==== in2.d.ts (1 errors) ====
     import a = A;
            ~
diff --git a/tests/baselines/reference/project/declareVariableCollision/node/declareVariableCollision.errors.txt b/tests/baselines/reference/project/declareVariableCollision/node/declareVariableCollision.errors.txt
index 5dc0a63d7eb11..64ec399fabf71 100644
--- a/tests/baselines/reference/project/declareVariableCollision/node/declareVariableCollision.errors.txt
+++ b/tests/baselines/reference/project/declareVariableCollision/node/declareVariableCollision.errors.txt
@@ -1,3 +1,4 @@
+in1.d.ts(1,8): error TS2300: Duplicate identifier 'a'.
 in2.d.ts(1,8): error TS2300: Duplicate identifier 'a'.
 
 
@@ -14,8 +15,10 @@ in2.d.ts(1,8): error TS2300: Duplicate identifier 'a'.
             class MyClass{ }
         }
     }
-==== in1.d.ts (0 errors) ====
+==== in1.d.ts (1 errors) ====
     import a = A;
+           ~
+!!! error TS2300: Duplicate identifier 'a'.
 ==== in2.d.ts (1 errors) ====
     import a = A;
            ~
diff --git a/tests/cases/compiler/constDeclarationShadowedByVarDeclaration.ts b/tests/cases/compiler/constDeclarationShadowedByVarDeclaration.ts
new file mode 100644
index 0000000000000..a4d392338477a
--- /dev/null
+++ b/tests/cases/compiler/constDeclarationShadowedByVarDeclaration.ts
@@ -0,0 +1,24 @@
+// @target: ES6
+
+// Error as declaration of var would cause a write to the const value
+var x = 0;
+{
+    const x = 0;
+
+    var x = 0;
+}
+
+
+var y = 0;
+{
+    const y = 0;
+    {
+        var y = 0;
+    }
+}
+
+
+{
+  const z = 0;
+  var z = 0
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarationShadowedByVarDeclaration2.ts b/tests/cases/compiler/constDeclarationShadowedByVarDeclaration2.ts
new file mode 100644
index 0000000000000..98930953996bb
--- /dev/null
+++ b/tests/cases/compiler/constDeclarationShadowedByVarDeclaration2.ts
@@ -0,0 +1,9 @@
+// @target: ES6
+
+// No errors, const declaration is not shadowed
+function outer() {
+    const x = 0;
+    function inner() {
+        var x = "inner";
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarationShadowedByVarDeclaration3.ts b/tests/cases/compiler/constDeclarationShadowedByVarDeclaration3.ts
new file mode 100644
index 0000000000000..5b4229a8e5469
--- /dev/null
+++ b/tests/cases/compiler/constDeclarationShadowedByVarDeclaration3.ts
@@ -0,0 +1,9 @@
+// Ensure only checking for const declarations shadowed by vars
+class Rule {
+    public regex: RegExp = new RegExp('');
+    public name: string = '';
+
+    constructor(name: string) {
+        this.name = name;
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarations-access.ts b/tests/cases/compiler/constDeclarations-access.ts
new file mode 100644
index 0000000000000..665d6753a6df6
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-access.ts
@@ -0,0 +1,7 @@
+// @target: ES6
+
+// @Filename: file1.ts
+const x = 0
+
+// @Filename: file2.ts
+x++;
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarations-access2.ts b/tests/cases/compiler/constDeclarations-access2.ts
new file mode 100644
index 0000000000000..e3f83940d1de0
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-access2.ts
@@ -0,0 +1,40 @@
+// @target: ES6
+
+const x = 0
+
+// Errors
+x = 1;
+x += 2;
+x -= 3;
+x *= 4;
+x /= 5;
+x %= 6;
+x <<= 7;
+x >>= 8;
+x >>>= 9;
+x &= 10;
+x |= 11;
+x ^= 12;
+
+x++;
+x--;
+++x;
+--x;
+
+++((x));
+
+// OK
+var a = x + 1;
+
+function f(v: number) { }
+f(x);
+
+if (x) { }
+
+x;
+(x);
+
+-x;
++x;
+
+x.toString();
diff --git a/tests/cases/compiler/constDeclarations-access3.ts b/tests/cases/compiler/constDeclarations-access3.ts
new file mode 100644
index 0000000000000..370288dab9734
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-access3.ts
@@ -0,0 +1,45 @@
+// @target: ES6
+
+
+module M {
+    export const x = 0;
+}
+
+// Errors
+M.x = 1;
+M.x += 2;
+M.x -= 3;
+M.x *= 4;
+M.x /= 5;
+M.x %= 6;
+M.x <<= 7;
+M.x >>= 8;
+M.x >>>= 9;
+M.x &= 10;
+M.x |= 11;
+M.x ^= 12;
+
+M.x++;
+M.x--;
+++M.x;
+--M.x;
+
+++((M.x));
+
+M["x"] = 0;
+
+// OK
+var a = M.x + 1;
+
+function f(v: number) { }
+f(M.x);
+
+if (M.x) { }
+
+M.x;
+(M.x);
+
+-M.x;
++M.x;
+
+M.x.toString();
diff --git a/tests/cases/compiler/constDeclarations-access4.ts b/tests/cases/compiler/constDeclarations-access4.ts
new file mode 100644
index 0000000000000..492f6a31d6df7
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-access4.ts
@@ -0,0 +1,45 @@
+// @target: ES6
+
+
+declare module M {
+    const x: number;
+}
+
+// Errors
+M.x = 1;
+M.x += 2;
+M.x -= 3;
+M.x *= 4;
+M.x /= 5;
+M.x %= 6;
+M.x <<= 7;
+M.x >>= 8;
+M.x >>>= 9;
+M.x &= 10;
+M.x |= 11;
+M.x ^= 12;
+
+M.x++;
+M.x--;
+++M.x;
+--M.x;
+
+++((M.x));
+
+M["x"] = 0;
+
+// OK
+var a = M.x + 1;
+
+function f(v: number) { }
+f(M.x);
+
+if (M.x) { }
+
+M.x;
+(M.x);
+
+-M.x;
++M.x;
+
+M.x.toString();
diff --git a/tests/cases/compiler/constDeclarations-access5.ts b/tests/cases/compiler/constDeclarations-access5.ts
new file mode 100644
index 0000000000000..1590d9289ef71
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-access5.ts
@@ -0,0 +1,48 @@
+// @target: ES6
+// @module: amd
+
+
+// @Filename: constDeclarations_access_1.ts
+export const x = 0;
+
+// @Filename: constDeclarations_access_2.ts
+///<reference path='constDeclarations_access_1.ts'/>
+import m = require('constDeclarations_access_1');
+// Errors
+m.x = 1;
+m.x += 2;
+m.x -= 3;
+m.x *= 4;
+m.x /= 5;
+m.x %= 6;
+m.x <<= 7;
+m.x >>= 8;
+m.x >>>= 9;
+m.x &= 10;
+m.x |= 11;
+m.x ^= 12;
+m
+m.x++;
+m.x--;
+++m.x;
+--m.x;
+
+++((m.x));
+
+m["x"] = 0;
+
+// OK
+var a = m.x + 1;
+
+function f(v: number) { }
+f(m.x);
+
+if (m.x) { }
+
+m.x;
+(m.x);
+
+-m.x;
++m.x;
+
+m.x.toString();
diff --git a/tests/cases/compiler/constDeclarations-ambient-errors.ts b/tests/cases/compiler/constDeclarations-ambient-errors.ts
new file mode 100644
index 0000000000000..c07bfb01810a5
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-ambient-errors.ts
@@ -0,0 +1,11 @@
+// @target: ES6
+
+// error: no intialization expected in ambient declarations
+declare const c1: boolean = true;
+declare const c2: number = 0;
+declare const c3 = null, c4 :string = "", c5: any = 0;
+
+declare module M {
+    const c6 = 0;
+    const c7: number = 7;
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarations-ambient.ts b/tests/cases/compiler/constDeclarations-ambient.ts
new file mode 100644
index 0000000000000..dcd4cb9fc726d
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-ambient.ts
@@ -0,0 +1,11 @@
+// @target: ES6
+
+// No error
+declare const c1: boolean;
+declare const c2: number;
+declare const c3, c4 :string, c5: any;
+
+declare module M {
+    const c6;
+    const c7: number;
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarations-errors.ts b/tests/cases/compiler/constDeclarations-errors.ts
new file mode 100644
index 0000000000000..09dc0e9679068
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-errors.ts
@@ -0,0 +1,18 @@
+// @target: ES6
+
+// error, missing intialicer
+const c1;
+const c2: number;
+const c3, c4, c5 :string, c6;  // error, missing initialicer
+
+// error, can not be unintalized
+for(const c in {}) { }
+
+// error, assigning to a const
+for(const c8 = 0; c8 < 1; c8++) { }
+
+// error, can not be unintalized
+for(const c9; c9 < 1;) { }
+
+// error, can not be unintalized
+for(const c10 = 0, c11; c10 < 1;) { }
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarations-es5.ts b/tests/cases/compiler/constDeclarations-es5.ts
new file mode 100644
index 0000000000000..0da824a7396d8
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-es5.ts
@@ -0,0 +1,5 @@
+// @target: ES5
+
+const z7 = false;
+const z8: number = 23;
+const z9 = 0, z10 :string = "", z11 = null;
diff --git a/tests/cases/compiler/constDeclarations-invalidContexts.ts b/tests/cases/compiler/constDeclarations-invalidContexts.ts
new file mode 100644
index 0000000000000..3da91a7d1d75c
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-invalidContexts.ts
@@ -0,0 +1,33 @@
+// @target: ES6
+
+// Errors, const must be defined inside a block
+if (true) 
+    const c1 = 0;
+else 
+    const c2 = 0;
+
+while (true) 
+    const c3 = 0;
+
+do 
+    const c4 = 0;
+while (true);
+
+var obj;
+with (obj) 
+    const c5 = 0;
+
+for (var i = 0; i < 10; i++)
+    const c6 = 0;
+
+for (var i2 in {}) 
+    const c7 = 0;
+
+if (true) 
+    label: const c8 = 0;
+
+while (false)
+    label2: label3: label4: const c9 = 0;
+
+
+
diff --git a/tests/cases/compiler/constDeclarations-scopes.ts b/tests/cases/compiler/constDeclarations-scopes.ts
new file mode 100644
index 0000000000000..d0c1df425b618
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-scopes.ts
@@ -0,0 +1,148 @@
+// @target: ES6
+
+// global
+const c = "string";
+
+var n: number;
+
+// Control flow statements with blocks
+if (true) { 
+    const c = 0;
+    n = c;
+}
+else { 
+    const c = 0;
+    n = c;
+}
+
+while (true) { 
+    const c = 0;
+    n = c;
+}
+
+do { 
+   const c = 0;
+    n = c;
+} while (true);
+
+var obj;
+with (obj) {
+    const c = 0;
+    n = c;
+}
+
+for (var i = 0; i < 10; i++) {
+    const c = 0;
+    n = c;
+}
+
+for (var i2 in {}) {
+    const c = 0;
+    n = c;
+}
+
+if (true) {
+    label: const c = 0;
+    n = c;
+}
+
+while (false) {
+    label2: label3: label4: const c = 0;
+    n = c;
+}
+
+// Try/catch/finally
+try {
+    const c = 0;
+    n = c;
+}
+catch (e) {
+    const c = 0;
+    n = c;
+}
+finally {
+    const c = 0;
+    n = c;
+}
+
+// Switch
+switch (0) {
+    case 0:
+        const c = 0;
+        n = c;
+        break;
+}
+
+// blocks
+{
+    const c = 0;
+    n = c;
+    {
+        const c = false;
+        var b: boolean = c;
+    }
+}
+
+// functions
+
+function F() {
+    const c = 0;
+    n = c;
+}
+
+var F2 = () => {
+    const c = 0;
+    n = c;
+};
+
+var F3 = function () {
+    const c = 0;
+    n = c;
+};
+
+// modules
+module m {
+    const c = 0;
+    n = c;
+
+    {
+       const c = false;
+       var b2: boolean = c;
+    }
+}
+
+// methods
+class C {
+    constructor() {
+        const c = 0;
+        n = c;
+    }
+
+    method() {
+        const c = 0;
+        n = c;
+    }
+
+    get v() {
+        const c = 0;
+        n = c;
+        return n;
+    }
+
+    set v(value) {
+        const c = 0;
+        n = c;
+    }
+}
+
+// object literals
+var o = {
+    f() {
+        const c = 0;
+        n = c;
+    },
+    f2: () => {
+        const c = 0;
+        n = c;
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarations-scopes2.ts b/tests/cases/compiler/constDeclarations-scopes2.ts
new file mode 100644
index 0000000000000..fe0ab16409a98
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-scopes2.ts
@@ -0,0 +1,15 @@
+// @target: ES6
+
+// global
+const c = "string";
+
+var n: number;
+var b: boolean;
+
+// for scope
+for (const c = 0; c < 10; n = c ) {
+    // for block
+    const c = false;
+    b = c;
+}
+
diff --git a/tests/cases/compiler/constDeclarations-useBeforeDefinition.ts b/tests/cases/compiler/constDeclarations-useBeforeDefinition.ts
new file mode 100644
index 0000000000000..ec793fda4846f
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-useBeforeDefinition.ts
@@ -0,0 +1,12 @@
+// @target: ES6
+
+{
+    c1;
+    const c1 = 0;
+}
+
+var v1;
+{
+    v1;
+    const v1 = 0;
+}
diff --git a/tests/cases/compiler/constDeclarations-useBeforeDefinition2.ts b/tests/cases/compiler/constDeclarations-useBeforeDefinition2.ts
new file mode 100644
index 0000000000000..c34bb4012bfc2
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-useBeforeDefinition2.ts
@@ -0,0 +1,8 @@
+// @target: ES6
+// @out: out.js
+
+// @Filename: file1.ts
+c;
+
+// @Filename: file2.ts
+const c = 0;
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarations-validContexts.ts b/tests/cases/compiler/constDeclarations-validContexts.ts
new file mode 100644
index 0000000000000..ffde8e45d6fa1
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations-validContexts.ts
@@ -0,0 +1,124 @@
+// @target: ES6
+
+
+// Control flow statements with blocks
+if (true) { 
+    const c1 = 0;
+}
+else { 
+    const c2 = 0;
+}
+
+while (true) { 
+    const c3 = 0;
+}
+
+do { 
+    const c4 = 0;
+} while (true);
+
+var obj;
+with (obj) {
+    const c5 = 0;
+}
+
+for (var i = 0; i < 10; i++) {
+    const c6 = 0;
+}
+
+for (var i2 in {}) {
+    const c7 = 0;
+}
+
+if (true) {
+    label: const c8 = 0;
+}
+
+while (false) {
+    label2: label3: label4: const c9 = 0;
+}
+
+// Try/catch/finally
+try {
+    const c10 = 0;
+}
+catch (e) {
+    const c11 = 0;
+}
+finally {
+    const c12 = 0;
+}
+
+// Switch
+switch (0) {
+    case 0:
+        const c13 = 0;
+        break;
+    default:
+        const c14 = 0;
+        break;
+}
+
+// blocks
+{
+    const c15 = 0;
+    {
+        const c16 = 0
+        label17: const c17 = 0;
+    }
+}
+
+// global
+const c18 = 0;
+
+// functions
+function F() {
+    const c19 = 0;
+}
+
+var F2 = () => {
+    const c20 = 0;
+};
+
+var F3 = function () {
+    const c21 = 0;
+};
+
+// modules
+module m {
+    const c22 = 0;
+
+    {
+          const c23 = 0;
+    }
+}
+
+// methods
+class C {
+    constructor() {
+        const c24 = 0;
+    }
+
+    method() {
+        const c25 = 0;
+    }
+
+    get v() {
+        const c26 = 0;
+        return c26; 
+    }
+
+    set v(value) {
+        const c27 = value;
+    }
+}
+
+// object literals
+var o = {
+    f() {
+        const c28 = 0;
+    },
+    f2: () => {
+        const c29 = 0;
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarations.ts b/tests/cases/compiler/constDeclarations.ts
new file mode 100644
index 0000000000000..2b8563b340a21
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations.ts
@@ -0,0 +1,13 @@
+// @target: ES6
+// @declaration: true
+
+// No error
+const c1 = false;
+const c2: number = 23;
+const c3 = 0, c4 :string = "", c5 = null;
+
+
+for(const c4 = 0; c4 < 9; ) { break; }
+
+
+for(const c5 = 0, c6 = 0; c5 < c6; ) { break; }
\ No newline at end of file
diff --git a/tests/cases/compiler/constDeclarations2.ts b/tests/cases/compiler/constDeclarations2.ts
new file mode 100644
index 0000000000000..a221c3563bae0
--- /dev/null
+++ b/tests/cases/compiler/constDeclarations2.ts
@@ -0,0 +1,9 @@
+// @target: ES6
+// @declaration: true
+
+// No error
+module M {
+    export const c1 = false;
+    export const c2: number = 23;
+    export const c3 = 0, c4 :string = "", c5 = null;
+}
diff --git a/tests/cases/compiler/es6-amd.ts b/tests/cases/compiler/es6-amd.ts
new file mode 100644
index 0000000000000..a5fb99a86051d
--- /dev/null
+++ b/tests/cases/compiler/es6-amd.ts
@@ -0,0 +1,17 @@
+// @target: ES6
+// @sourcemap: false
+// @declaration: false
+// @module: amd
+
+class A
+{
+    constructor ()
+    {
+
+    }
+
+    public B()
+    {
+        return 42;
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/es6-declaration-amd.ts b/tests/cases/compiler/es6-declaration-amd.ts
new file mode 100644
index 0000000000000..1dcfeca84979e
--- /dev/null
+++ b/tests/cases/compiler/es6-declaration-amd.ts
@@ -0,0 +1,17 @@
+// @target: ES6
+// @sourcemap: false
+// @declaration: true
+// @module: amd
+
+class A
+{
+    constructor ()
+    {
+
+    }
+
+    public B()
+    {
+        return 42;
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/es6-sourcemap-amd.ts b/tests/cases/compiler/es6-sourcemap-amd.ts
new file mode 100644
index 0000000000000..c00a697de940b
--- /dev/null
+++ b/tests/cases/compiler/es6-sourcemap-amd.ts
@@ -0,0 +1,16 @@
+// @target: ES6
+// @sourcemap: true
+// @module: amd
+
+class A
+{
+    constructor ()
+    {
+
+    }
+
+    public B()
+    {
+        return 42;
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/functionTypeArgumentArrayAssignment.ts b/tests/cases/compiler/functionTypeArgumentArrayAssignment.ts
index 77fbb74d7ad3e..91cf2d551b9d4 100644
--- a/tests/cases/compiler/functionTypeArgumentArrayAssignment.ts
+++ b/tests/cases/compiler/functionTypeArgumentArrayAssignment.ts
@@ -1,8 +1,10 @@
-interface Array<T> {
-	foo: T;
-	length: number;
-}
+module test {
+    interface Array<T> {
+        foo: T;
+        length: number;
+    }
 
-function map<U>() {
-var ys: U[] = [];
+    function map<U>() {
+        var ys: U[] = [];
+    }
 }
diff --git a/tests/cases/compiler/instanceofOperator.ts b/tests/cases/compiler/instanceofOperator.ts
index 60b724149ce5d..f9b304de11367 100644
Binary files a/tests/cases/compiler/instanceofOperator.ts and b/tests/cases/compiler/instanceofOperator.ts differ
diff --git a/tests/cases/compiler/letDeclarations-access.ts b/tests/cases/compiler/letDeclarations-access.ts
new file mode 100644
index 0000000000000..6ed655f1cb25c
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-access.ts
@@ -0,0 +1,38 @@
+// @target: ES6
+
+let x = 0
+
+// No errors
+
+x = 1;
+x += 2;
+x -= 3;
+x *= 4;
+x /= 5;
+x %= 6;
+x <<= 7;
+x >>= 8;
+x >>>= 9;
+x &= 10;
+x |= 11;
+x ^= 12;
+
+x++;
+x--;
+++x;
+--x;
+
+var a = x + 1;
+
+function f(v: number) { }
+f(x);
+
+if (x) { }
+
+x;
+(x);
+
+-x;
++x;
+
+x.toString();
diff --git a/tests/cases/compiler/letDeclarations-es5.ts b/tests/cases/compiler/letDeclarations-es5.ts
new file mode 100644
index 0000000000000..b115c260a915c
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-es5.ts
@@ -0,0 +1,13 @@
+// @target: ES5
+
+let l1;
+let l2: number;
+let l3, l4, l5 :string, l6;
+
+let l7 = false;
+let l8: number = 23;
+let l9 = 0, l10 :string = "", l11 = null;
+
+for(let l11 in {}) { }
+
+for(let l12 = 0; l12 < 9; l12++) { }
diff --git a/tests/cases/compiler/letDeclarations-invalidContexts.ts b/tests/cases/compiler/letDeclarations-invalidContexts.ts
new file mode 100644
index 0000000000000..4d165ba2cda0e
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-invalidContexts.ts
@@ -0,0 +1,33 @@
+// @target: ES6
+
+// Errors, let must be defined inside a block
+if (true) 
+    let l1 = 0;
+else 
+    let l2 = 0;
+
+while (true) 
+    let l3 = 0;
+
+do 
+    let l4 = 0;
+while (true);
+
+var obj;
+with (obj) 
+    let l5 = 0;
+
+for (var i = 0; i < 10; i++)
+    let l6 = 0;
+
+for (var i2 in {}) 
+    let l7 = 0;
+
+if (true) 
+    label: let l8 = 0;
+
+while (false)
+    label2: label3: label4: let l9 = 0;
+
+
+
diff --git a/tests/cases/compiler/letDeclarations-scopes-duplicates.ts b/tests/cases/compiler/letDeclarations-scopes-duplicates.ts
new file mode 100644
index 0000000000000..841b55af1685b
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-scopes-duplicates.ts
@@ -0,0 +1,77 @@
+// @target: ES6
+
+// Errors: redeclaration
+let var1 = 0;
+let var1 = 0; // error
+
+let var2 = 0;
+const var2 = 0;
+
+const var3 = 0;
+let var3 = 0;
+
+const var4 = 0;
+const var4 = 0;
+
+var var5 = 0;
+let var5 = 0;
+
+let var6 = 0;
+var var6 = 0;
+
+{
+    let var7 = 0;
+    let var7 = 0;
+    {
+        let var8 = 0;
+        const var8 = 0;
+    }
+}
+
+switch (0) {
+    default:
+        let var9 = 0;
+        let var9 = 0;
+}
+
+try {
+    const var10 = 0;
+    const var10 = 0;
+}
+catch (e) {
+    let var11 = 0;
+    let var11 = 0;
+}
+
+function F1() {
+    let var12;
+    let var12;
+}
+
+// OK
+var var20 = 0;
+
+var var20 = 0
+{
+    let var20 = 0;
+    {
+        let var20 = 0;
+    }
+}
+
+switch (0) {
+    default:
+        let var20 = 0;
+}
+
+try {
+    let var20 = 0;
+}
+catch (e) {
+    let var20 = 0;
+}
+
+function F() {
+    let var20;
+}
+
diff --git a/tests/cases/compiler/letDeclarations-scopes-duplicates2.ts b/tests/cases/compiler/letDeclarations-scopes-duplicates2.ts
new file mode 100644
index 0000000000000..40ddc14fc3f1a
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-scopes-duplicates2.ts
@@ -0,0 +1,7 @@
+// @target: ES6
+
+// @Filename: file1.ts
+let var1 = 0;
+
+// @Filename: file2.ts
+let var1 = 0;
\ No newline at end of file
diff --git a/tests/cases/compiler/letDeclarations-scopes-duplicates3.ts b/tests/cases/compiler/letDeclarations-scopes-duplicates3.ts
new file mode 100644
index 0000000000000..1f10efa53850c
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-scopes-duplicates3.ts
@@ -0,0 +1,7 @@
+// @target: ES6
+
+// @Filename: file1.ts
+let var1 = 0;
+
+// @Filename: file2.ts
+const var1 = 0;
\ No newline at end of file
diff --git a/tests/cases/compiler/letDeclarations-scopes-duplicates4.ts b/tests/cases/compiler/letDeclarations-scopes-duplicates4.ts
new file mode 100644
index 0000000000000..150d434a2bc14
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-scopes-duplicates4.ts
@@ -0,0 +1,7 @@
+// @target: ES6
+
+// @Filename: file1.ts
+const var1 = 0;
+
+// @Filename: file2.ts
+let var1 = 0;
\ No newline at end of file
diff --git a/tests/cases/compiler/letDeclarations-scopes-duplicates5.ts b/tests/cases/compiler/letDeclarations-scopes-duplicates5.ts
new file mode 100644
index 0000000000000..da24985349910
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-scopes-duplicates5.ts
@@ -0,0 +1,7 @@
+// @target: ES6
+
+// @Filename: file1.ts
+const var1 = 0;
+
+// @Filename: file2.ts
+const var1 = 0;
\ No newline at end of file
diff --git a/tests/cases/compiler/letDeclarations-scopes-duplicates6.ts b/tests/cases/compiler/letDeclarations-scopes-duplicates6.ts
new file mode 100644
index 0000000000000..f71b7623790cc
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-scopes-duplicates6.ts
@@ -0,0 +1,7 @@
+// @target: ES6
+
+// @Filename: file1.ts
+var var1 = 0;
+
+// @Filename: file2.ts
+let var1 = 0;
\ No newline at end of file
diff --git a/tests/cases/compiler/letDeclarations-scopes-duplicates7.ts b/tests/cases/compiler/letDeclarations-scopes-duplicates7.ts
new file mode 100644
index 0000000000000..829fda0c927bc
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-scopes-duplicates7.ts
@@ -0,0 +1,7 @@
+// @target: ES6
+
+// @Filename: file1.ts
+let var1 = 0;
+
+// @Filename: file2.ts
+var var1 = 0;
\ No newline at end of file
diff --git a/tests/cases/compiler/letDeclarations-scopes.ts b/tests/cases/compiler/letDeclarations-scopes.ts
new file mode 100644
index 0000000000000..93f4ce5b4ed0f
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-scopes.ts
@@ -0,0 +1,158 @@
+// @target: ES6
+
+// global
+let l = "string";
+
+var n: number;
+
+// Control flow statements with blocks
+if (true) {
+    let l = 0;
+    n = l;
+}
+else {
+    let l = 0;
+    n = l;
+}
+
+while (true) {
+    let l = 0;
+    n = l;
+}
+
+do {
+   let l = 0;
+    n = l;
+} while (true);
+
+var obj;
+with (obj) {
+    let l = 0;
+    n = l;
+}
+
+for (var i = 0; i < 10; i++) {
+    let l = 0;
+    n = l;
+}
+
+for (var i2 in {}) {
+    let l = 0;
+    n = l;
+}
+
+if (true) {
+    label: let l = 0;
+    n = l;
+}
+
+while (false) {
+    label2: label3: label4: let l = 0;
+    n = l;
+}
+
+for (let l = 0; n = l; l++) {
+    let l = true;
+    var b3: boolean = l;
+}
+
+for (let l in {}) {
+
+}
+
+// Try/catch/finally
+try {
+    let l = 0;
+    n = l;
+}
+catch (e) {
+    let l = 0;
+    n = l;
+}
+finally {
+    let l = 0;
+    n = l;
+}
+
+// Switch
+switch (0) {
+    case 0:
+        let l = 0;
+        n = l;
+        break;
+}
+
+// blocks
+{
+    let l = 0;
+    n = l;
+    {
+        let l = false;
+        var b: boolean = l;
+    }
+}
+
+// functions
+function F() {
+    let l = 0;
+    n = l;
+}
+
+var F2 = () => {
+    let l = 0;
+    n = l;
+};
+
+var F3 = function () {
+    let l = 0;
+    n = l;
+};
+
+// modules
+module m {
+    let l = 0;
+    n = l;
+
+    {
+       let l = false;
+       var b2: boolean = l;
+    }
+
+    lable: let l2 = 0;
+}
+
+// methods
+class C {
+    constructor() {
+        let l = 0;
+        n = l;
+    }
+
+    method() {
+        let l = 0;
+        n = l;
+    }
+
+    get v() {
+        let l = 0;
+        n = l;
+        return n;
+    }
+
+    set v(value) {
+        let l = 0;
+        n = l;
+    }
+}
+
+// object literals
+var o = {
+    f() {
+        let l = 0;
+        n = l;
+    },
+    f2: () => {
+        let l = 0;
+        n = l;
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/letDeclarations-scopes2.ts b/tests/cases/compiler/letDeclarations-scopes2.ts
new file mode 100644
index 0000000000000..6f1200a0cb237
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-scopes2.ts
@@ -0,0 +1,27 @@
+// @target: ES6
+
+let global = 0;
+
+{ 
+    let local = 0;
+
+    local;  // OK
+    global; // OK
+    local2; // Error
+
+    {
+        let local2 = 0;
+
+        local;  // OK
+        global; // OK
+        local2; // OK
+    } 
+
+    local;  // OK
+    global; // OK
+    local2; // Error
+}
+
+local;  // Error
+global; // OK
+local2; // Error
diff --git a/tests/cases/compiler/letDeclarations-useBeforeDefinition.ts b/tests/cases/compiler/letDeclarations-useBeforeDefinition.ts
new file mode 100644
index 0000000000000..671762d4a45ea
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-useBeforeDefinition.ts
@@ -0,0 +1,12 @@
+// @target: ES6
+
+{
+    l1;
+    let l1;
+}
+
+var v1;
+{
+    v1;
+    let v1 = 0;
+}
diff --git a/tests/cases/compiler/letDeclarations-useBeforeDefinition2.ts b/tests/cases/compiler/letDeclarations-useBeforeDefinition2.ts
new file mode 100644
index 0000000000000..a6cbc729b94c4
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-useBeforeDefinition2.ts
@@ -0,0 +1,8 @@
+// @target: ES6
+// @out: out.js
+
+// @Filename: file1.ts
+l;
+
+// @Filename: file2.ts
+const l = 0;
\ No newline at end of file
diff --git a/tests/cases/compiler/letDeclarations-validContexts.ts b/tests/cases/compiler/letDeclarations-validContexts.ts
new file mode 100644
index 0000000000000..baedfa2644cb0
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations-validContexts.ts
@@ -0,0 +1,144 @@
+// @target: ES6
+
+
+// Control flow statements with blocks
+if (true) { 
+    let l1 = 0;
+}
+else { 
+    let l2 = 0;
+}
+
+while (true) { 
+    let l3 = 0;
+}
+
+do { 
+    let l4 = 0;
+} while (true);
+
+var obj;
+with (obj) {
+    let l5 = 0;
+}
+
+for (var i = 0; i < 10; i++) {
+    let l6 = 0;
+}
+
+for (var i2 in {}) {
+    let l7 = 0;
+}
+
+if (true) {
+    label: let l8 = 0;
+}
+
+while (false) {
+    label2: label3: label4: let l9 = 0;
+}
+
+// Try/catch/finally
+try {
+    let l10 = 0;
+}
+catch (e) {
+    let l11 = 0;
+}
+finally {
+    let l12 = 0;
+}
+
+// Switch
+switch (0) {
+    case 0:
+        let l13 = 0;
+        break;
+    default:
+        let l14 = 0;
+        break;
+}
+
+// blocks
+{
+    let l15 = 0;
+    {
+        let l16 = 0
+        label17: let l17 = 0;
+    }
+}
+
+// global
+let l18 = 0;
+
+// functions
+function F() {
+    let l19 = 0;
+}
+
+var F2 = () => {
+    let l20 = 0;
+};
+
+var F3 = function () {
+    let l21 = 0;
+};
+
+// modules
+module m {
+    let l22 = 0;
+
+    {
+          let l23 = 0;
+    }
+}
+
+// methods
+class C {
+    constructor() {
+        let l24 = 0;
+    }
+
+    method() {
+        let l25 = 0;
+    }
+
+    get v() {
+        let l26 = 0;
+        return l26; 
+    }
+
+    set v(value) {
+        let l27 = value;
+    }
+}
+
+// object literals
+var o = {
+    f() {
+        let l28 = 0;
+    },
+    f2: () => {
+        let l29 = 0;
+    }
+}
+
+// labels
+label: let l30 = 0;
+{
+    label2: let l31 = 0;
+}
+
+function f3() {
+    label: let l32 = 0;
+    {
+        label2: let l33 = 0;
+    }
+}
+
+module m3 {
+    label: let l34 = 0;
+    {
+        label2: let l35 = 0;
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/letDeclarations.ts b/tests/cases/compiler/letDeclarations.ts
new file mode 100644
index 0000000000000..e90e355ba68ac
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations.ts
@@ -0,0 +1,14 @@
+// @target: ES6
+// @declaration: true
+
+let l1;
+let l2: number;
+let l3, l4, l5 :string, l6;
+
+let l7 = false;
+let l8: number = 23;
+let l9 = 0, l10 :string = "", l11 = null;
+
+for(let l11 in {}) { }
+
+for(let l12 = 0; l12 < 9; l12++) { }
diff --git a/tests/cases/compiler/letDeclarations2.ts b/tests/cases/compiler/letDeclarations2.ts
new file mode 100644
index 0000000000000..e7e09f0849a3a
--- /dev/null
+++ b/tests/cases/compiler/letDeclarations2.ts
@@ -0,0 +1,7 @@
+// @target: ES6
+// @declaration: true
+
+module M {
+    let l1 = "s";
+    export let l2 = 0;
+}
\ No newline at end of file
diff --git a/tests/cases/conformance/parser/ecmascript5/parserOptionalTypeMembers1.ts b/tests/cases/conformance/parser/ecmascript5/parserOptionalTypeMembers1.ts
index fb3b96952feb3..331d0faed9e41 100644
--- a/tests/cases/conformance/parser/ecmascript5/parserOptionalTypeMembers1.ts
+++ b/tests/cases/conformance/parser/ecmascript5/parserOptionalTypeMembers1.ts
@@ -1,4 +1,4 @@
-interface PropertyDescriptor {
+interface PropertyDescriptor2 {
     configurable?: boolean;
     enumerable?: boolean;
     value?: any;
diff --git a/tests/cases/fourslash/completionEntryForConst.ts b/tests/cases/fourslash/completionEntryForConst.ts
new file mode 100644
index 0000000000000..f6b7cc42d63d7
--- /dev/null
+++ b/tests/cases/fourslash/completionEntryForConst.ts
@@ -0,0 +1,7 @@
+///<reference path="fourslash.ts" />
+
+////const c = "s";
+/////**/
+
+goTo.marker();
+verify.completionListContains("c", /*text*/ undefined, /*documentation*/ undefined, "constant");
\ No newline at end of file
diff --git a/tests/cases/fourslash/navbar_const.ts b/tests/cases/fourslash/navbar_const.ts
new file mode 100644
index 0000000000000..ede2a9cd1d8b6
--- /dev/null
+++ b/tests/cases/fourslash/navbar_const.ts
@@ -0,0 +1,13 @@
+/// <reference path="fourslash.ts" />
+
+//// {| "itemName": "c", "kind": "constant", "parentName": "" |}const c = 0;
+
+test.markers().forEach(marker => {
+    verify.getScriptLexicalStructureListContains(
+        marker.data.itemName,
+        marker.data.kind,
+        marker.fileName,
+        marker.data.parentName,
+        marker.data.isAdditionalRange,
+        marker.position);
+});
\ No newline at end of file
diff --git a/tests/cases/fourslash/quickInfoForConstDeclaration.ts b/tests/cases/fourslash/quickInfoForConstDeclaration.ts
new file mode 100644
index 0000000000000..dc234b040509f
--- /dev/null
+++ b/tests/cases/fourslash/quickInfoForConstDeclaration.ts
@@ -0,0 +1,6 @@
+/// <reference path='fourslash.ts' />
+
+////const /**/c = 0 ;
+
+goTo.marker();
+verify.quickInfoIs("(constant) c: number");
\ No newline at end of file