diff --git a/rxjava-core/src/main/java/rx/Observable.java b/rxjava-core/src/main/java/rx/Observable.java
index 53327b371d..9f5f399ed0 100644
--- a/rxjava-core/src/main/java/rx/Observable.java
+++ b/rxjava-core/src/main/java/rx/Observable.java
@@ -51,6 +51,7 @@
 import rx.operators.OperationFirstOrDefault;
 import rx.operators.OperationGroupBy;
 import rx.operators.OperationInterval;
+import rx.operators.OperationJoin;
 import rx.operators.OperationLast;
 import rx.operators.OperationMap;
 import rx.operators.OperationMaterialize;
@@ -5662,5 +5663,25 @@ private boolean isInternalImplementation(Object o) {
             return isInternal;
         }
     }
-
+    /**
+     * Correlates the elements of two sequences based on overlapping durations.
+     * @param right The right observable sequence to join elements for.
+     * @param leftDurationSelector A function to select the duration of each 
+     *                             element of this observable sequence, used to
+     *                             determine overlap.
+     * @param rightDurationSelector A function to select the duration of each
+     *                              element of the right observable sequence, 
+     *                              used to determine overlap.
+     * @param resultSelector A function invoked to compute a result element 
+     *                       for any two overlapping elements of the left and
+     *                       right observable sequences.
+     * @return An observable sequence that contains result elements computed
+     *         from source elements that have an overlapping duration.
+     * @see <a href='http://msdn.microsoft.com/en-us/library/hh229750.aspx'>MSDN: Observable.Join</a>
+     */
+    public <TRight, TLeftDuration, TRightDuration, R> Observable<R> join(Observable<TRight> right, Func1<T, Observable<TLeftDuration>> leftDurationSelector,
+            Func1<TRight, Observable<TRightDuration>> rightDurationSelector,
+            Func2<T, TRight, R> resultSelector) {
+        return create(new OperationJoin<T, TRight, TLeftDuration, TRightDuration, R>(this, right, leftDurationSelector, rightDurationSelector, resultSelector));
+    }
 }
diff --git a/rxjava-core/src/main/java/rx/operators/OperationJoin.java b/rxjava-core/src/main/java/rx/operators/OperationJoin.java
new file mode 100644
index 0000000000..b75b8498b0
--- /dev/null
+++ b/rxjava-core/src/main/java/rx/operators/OperationJoin.java
@@ -0,0 +1,277 @@
+/**
+ * Copyright 2013 Netflix, Inc.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package rx.operators;
+
+import java.util.HashMap;
+import java.util.Map;
+import rx.Observable;
+import rx.Observable.OnSubscribeFunc;
+import rx.Observer;
+import rx.Subscription;
+import rx.subscriptions.CompositeSubscription;
+import rx.subscriptions.SerialSubscription;
+import rx.util.functions.Func1;
+import rx.util.functions.Func2;
+
+/**
+ * Correlates the elements of two sequences based on overlapping durations.
+ */
+public class OperationJoin<TLeft, TRight, TLeftDuration, TRightDuration, R> implements OnSubscribeFunc<R> {
+    final Observable<TLeft> left;
+    final Observable<TRight> right;
+    final Func1<TLeft, Observable<TLeftDuration>> leftDurationSelector;
+    final Func1<TRight, Observable<TRightDuration>> rightDurationSelector;
+    final Func2<TLeft, TRight, R> resultSelector;
+    public OperationJoin(
+            Observable<TLeft> left, 
+            Observable<TRight> right,
+            Func1<TLeft, Observable<TLeftDuration>> leftDurationSelector,
+            Func1<TRight, Observable<TRightDuration>> rightDurationSelector,
+            Func2<TLeft, TRight, R> resultSelector) {
+        this.left = left;
+        this.right = right;
+        this.leftDurationSelector = leftDurationSelector;
+        this.rightDurationSelector = rightDurationSelector;
+        this.resultSelector = resultSelector;
+    }
+
+    @Override
+    public Subscription onSubscribe(Observer<? super R> t1) {
+        SerialSubscription cancel = new SerialSubscription();
+        ResultSink result = new ResultSink(t1, cancel);
+        cancel.setSubscription(result.run());
+        return cancel;
+    }
+    /** Manage the left and right sources. */
+    class ResultSink {
+        final Object gate = new Object();
+        final CompositeSubscription group = new CompositeSubscription();
+        boolean leftDone;
+        int leftId;
+        final Map<Integer, TLeft> leftMap = new HashMap<Integer, TLeft>();
+        boolean rightDone;
+        int rightId;
+        final Map<Integer, TRight> rightMap = new HashMap<Integer, TRight>();
+        final Observer<? super R> observer;
+        final Subscription cancel;
+        public ResultSink(Observer<? super R> observer, Subscription cancel) {
+            this.observer = observer;
+            this.cancel = cancel;
+        }
+        public Subscription run() {
+            SerialSubscription leftCancel = new SerialSubscription();
+            SerialSubscription rightCancel = new SerialSubscription();
+            
+            group.add(leftCancel);
+            group.add(rightCancel);
+            
+            leftCancel.setSubscription(left.subscribe(new LeftObserver(leftCancel)));
+            rightCancel.setSubscription(right.subscribe(new RightObserver(rightCancel)));
+            
+            return group;
+        }
+        /** Observes the left values. */
+        class LeftObserver implements Observer<TLeft> {
+            final Subscription self;
+            public LeftObserver(Subscription self) {
+                this.self = self;
+            }
+            protected void expire(int id, Subscription resource) {
+                synchronized (gate) {
+                    if (leftMap.remove(id) != null && leftMap.isEmpty() && leftDone) {
+                        observer.onCompleted();
+                        cancel.unsubscribe();
+                    }
+                }
+                group.remove(resource);
+            }
+            @Override
+            public void onNext(TLeft args) {
+                int id;
+                synchronized (gate) {
+                    id = leftId++;
+                    leftMap.put(id, args);
+                }
+                SerialSubscription md = new SerialSubscription();
+                group.add(md);
+                
+                Observable<TLeftDuration> duration;
+                try {
+                    duration = leftDurationSelector.call(args);
+                } catch (Throwable t) {
+                    observer.onError(t);
+                    cancel.unsubscribe();
+                    return;
+                }
+                
+                md.setSubscription(duration.subscribe(new LeftDurationObserver(id, md)));
+                
+                synchronized (gate) {
+                    for (TRight r : rightMap.values()) {
+                        R result;
+                        try {
+                            result = resultSelector.call(args, r);
+                        } catch (Throwable t) {
+                            observer.onError(t);
+                            cancel.unsubscribe();
+                            return;
+                        }
+                        observer.onNext(result);
+                    }
+                }
+            }
+            @Override
+            public void onError(Throwable e) {
+                synchronized (gate) {
+                    observer.onError(e);
+                    cancel.unsubscribe();
+                }
+            }
+            @Override
+            public void onCompleted() {
+                synchronized (gate) {
+                    leftDone = true;
+                    if (rightDone || leftMap.isEmpty()) {
+                        observer.onCompleted();
+                        cancel.unsubscribe();
+                    } else {
+                        self.unsubscribe();
+                    }
+                }
+            }
+            /** Observes the left duration. */
+            class LeftDurationObserver implements Observer<TLeftDuration> {
+                final int id;
+                final Subscription handle;
+                public LeftDurationObserver(int id, Subscription handle) {
+                    this.id = id;
+                    this.handle = handle;
+                }
+
+                @Override
+                public void onNext(TLeftDuration args) {
+                    expire(id, handle);
+                }
+
+                @Override
+                public void onError(Throwable e) {
+                    LeftObserver.this.onError(e);
+                }
+
+                @Override
+                public void onCompleted() {
+                    expire(id, handle);
+                }
+                
+            }
+        }
+        /** Observes the right values. */
+        class RightObserver implements Observer<TRight> {
+            final Subscription self;
+            public RightObserver(Subscription self) {
+                this.self = self;
+            }
+            void expire(int id, Subscription resource) {
+                synchronized (gate) {
+                    if (rightMap.remove(id) != null && rightMap.isEmpty() && rightDone) {
+                        observer.onCompleted();
+                        cancel.unsubscribe();
+                    }
+                }
+                group.remove(resource);
+            }
+            @Override
+            public void onNext(TRight args) {
+                int id = 0;
+                synchronized (gate) {
+                    id = rightId++;
+                    rightMap.put(id, args);
+                }
+                SerialSubscription md = new SerialSubscription();
+                group.add(md);
+                
+                Observable<TRightDuration> duration;
+                try {
+                    duration = rightDurationSelector.call(args);
+                } catch (Throwable t) {
+                    observer.onError(t);
+                    cancel.unsubscribe();
+                    return;
+                }
+                
+                md.setSubscription(duration.subscribe(new RightDurationObserver(id, md)));
+                
+                synchronized (gate) {
+                    for (TLeft lv : leftMap.values()) {
+                        R result;
+                        try {
+                            result = resultSelector.call(lv, args);
+                        } catch (Throwable t) {
+                            observer.onError(t);
+                            cancel.unsubscribe();
+                            return;
+                        }
+                        observer.onNext(result);
+                    }
+                }
+            }
+            @Override
+            public void onError(Throwable e) {
+                synchronized (gate) {
+                    observer.onError(e);
+                    cancel.unsubscribe();
+                }
+            }
+            @Override
+            public void onCompleted() {
+                synchronized (gate) {
+                    rightDone = true;
+                    if (leftDone || rightMap.isEmpty()) {
+                        observer.onCompleted();
+                        cancel.unsubscribe();
+                    } else {
+                        self.unsubscribe();
+                    }
+                }
+            }
+            /** Observe the right duration. */
+            class RightDurationObserver implements Observer<TRightDuration> {
+                final int id;
+                final Subscription handle;
+                public RightDurationObserver(int id, Subscription handle) {
+                    this.id = id;
+                    this.handle = handle;
+                }
+
+                @Override
+                public void onNext(TRightDuration args) {
+                    expire(id, handle);
+                }
+
+                @Override
+                public void onError(Throwable e) {
+                    RightObserver.this.onError(e);
+                }
+
+                @Override
+                public void onCompleted() {
+                    expire(id, handle);
+                }
+                
+            }
+        }
+    }
+}
diff --git a/rxjava-core/src/test/java/rx/operators/OperationJoinTest.java b/rxjava-core/src/test/java/rx/operators/OperationJoinTest.java
new file mode 100644
index 0000000000..8f841ebb50
--- /dev/null
+++ b/rxjava-core/src/test/java/rx/operators/OperationJoinTest.java
@@ -0,0 +1,302 @@
+/**
+ * Copyright 2013 Netflix, Inc.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package rx.operators;
+
+import java.util.Collection;
+import org.junit.Before;
+import org.junit.Test;
+import static org.mockito.Matchers.any;
+import org.mockito.Mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import org.mockito.MockitoAnnotations;
+import rx.Observable;
+import rx.Observer;
+import rx.subjects.PublishSubject;
+import rx.util.functions.Action1;
+import rx.util.functions.Func1;
+import rx.util.functions.Func2;
+
+public class OperationJoinTest {
+    @Mock
+    Observer<Object> observer;
+    
+    Func2<Integer, Integer, Integer> add = new Func2<Integer, Integer, Integer>() {
+        @Override
+        public Integer call(Integer t1, Integer t2) {
+            return t1 + t2;
+        }
+    };
+    <T> Func1<Integer, Observable<T>> just(final Observable<T> observable) {
+        return new Func1<Integer, Observable<T>>() {
+            @Override
+            public Observable<T> call(Integer t1) {
+                return observable;
+            }
+        };
+    }
+    @Before
+    public void before() {
+        MockitoAnnotations.initMocks(this);
+    }
+    @Test
+    public void normal1() {
+        PublishSubject<Integer> source1 = PublishSubject.create();
+        PublishSubject<Integer> source2 = PublishSubject.create();
+        
+        Observable<Integer> m = source1.join(source2, 
+                just(Observable.never()), 
+                just(Observable.never()), add);
+
+        m.subscribe(observer);
+        
+        source1.onNext(1);
+        source1.onNext(2);
+        source1.onNext(4);
+        
+        source2.onNext(16);
+        source2.onNext(32);
+        source2.onNext(64);
+        
+        source1.onCompleted();
+        source2.onCompleted();
+        
+        verify(observer, times(1)).onNext(17);
+        verify(observer, times(1)).onNext(18);
+        verify(observer, times(1)).onNext(20);
+        verify(observer, times(1)).onNext(33);
+        verify(observer, times(1)).onNext(34);
+        verify(observer, times(1)).onNext(36);
+        verify(observer, times(1)).onNext(65);
+        verify(observer, times(1)).onNext(66);
+        verify(observer, times(1)).onNext(68);
+        
+        verify(observer, times(1)).onCompleted();
+        verify(observer, never()).onError(any(Throwable.class));
+    }
+    @Test
+    public void normal1WithDuration() {
+        PublishSubject<Integer> source1 = PublishSubject.create();
+        PublishSubject<Integer> source2 = PublishSubject.create();
+
+        PublishSubject<Integer> duration1 = PublishSubject.create();
+        
+        Observable<Integer> m = source1.join(source2, 
+                just(duration1), 
+                just(Observable.never()), add);
+        m.subscribe(observer);
+
+        source1.onNext(1);
+        source1.onNext(2);
+        source2.onNext(16);
+        
+        duration1.onNext(1);
+        
+        source1.onNext(4);
+        source1.onNext(8);
+        
+        source1.onCompleted();
+        source2.onCompleted();
+        
+        verify(observer, times(1)).onNext(17);
+        verify(observer, times(1)).onNext(18);
+        verify(observer, times(1)).onNext(20);
+        verify(observer, times(1)).onNext(24);
+        
+        verify(observer, times(1)).onCompleted();
+        verify(observer, never()).onError(any(Throwable.class));
+        
+    }
+    @Test
+    public void normal2() {
+        PublishSubject<Integer> source1 = PublishSubject.create();
+        PublishSubject<Integer> source2 = PublishSubject.create();
+        
+        Observable<Integer> m = source1.join(source2, 
+                just(Observable.never()), 
+                just(Observable.never()), add);
+
+        m.subscribe(observer);
+        
+        source1.onNext(1);
+        source1.onNext(2);
+        source1.onCompleted();
+        
+        source2.onNext(16);
+        source2.onNext(32);
+        source2.onNext(64);
+        
+        source2.onCompleted();
+        
+        verify(observer, times(1)).onNext(17);
+        verify(observer, times(1)).onNext(18);
+        verify(observer, times(1)).onNext(33);
+        verify(observer, times(1)).onNext(34);
+        verify(observer, times(1)).onNext(65);
+        verify(observer, times(1)).onNext(66);
+        
+        verify(observer, times(1)).onCompleted();
+        verify(observer, never()).onError(any(Throwable.class));
+    }
+    @Test
+    public void leftThrows() {
+        PublishSubject<Integer> source1 = PublishSubject.create();
+        PublishSubject<Integer> source2 = PublishSubject.create();
+        
+        Observable<Integer> m = source1.join(source2, 
+                just(Observable.never()), 
+                just(Observable.never()), add);
+
+        m.subscribe(observer);
+
+        source2.onNext(1);
+        source1.onError(new RuntimeException("Forced failure"));
+        
+        verify(observer, times(1)).onError(any(Throwable.class));
+        verify(observer, never()).onCompleted();
+        verify(observer, never()).onNext(any());
+    }
+    @Test
+    public void rightThrows() {
+        PublishSubject<Integer> source1 = PublishSubject.create();
+        PublishSubject<Integer> source2 = PublishSubject.create();
+        
+        Observable<Integer> m = source1.join(source2, 
+                just(Observable.never()), 
+                just(Observable.never()), add);
+
+        m.subscribe(observer);
+
+        source1.onNext(1);
+        source2.onError(new RuntimeException("Forced failure"));
+        
+        verify(observer, times(1)).onError(any(Throwable.class));
+        verify(observer, never()).onCompleted();
+        verify(observer, never()).onNext(any());
+    }
+    @Test
+    public void leftDurationThrows() {
+        PublishSubject<Integer> source1 = PublishSubject.create();
+        PublishSubject<Integer> source2 = PublishSubject.create();
+
+        Observable<Integer> duration1 = Observable.<Integer>error(new RuntimeException("Forced failure"));
+        
+        Observable<Integer> m = source1.join(source2, 
+                just(duration1), 
+                just(Observable.never()), add);
+        m.subscribe(observer);
+
+        source1.onNext(1);
+        
+        
+        verify(observer, times(1)).onError(any(Throwable.class));
+        verify(observer, never()).onCompleted();
+        verify(observer, never()).onNext(any());
+    }
+    @Test
+    public void rightDurationThrows() {
+        PublishSubject<Integer> source1 = PublishSubject.create();
+        PublishSubject<Integer> source2 = PublishSubject.create();
+
+        Observable<Integer> duration1 = Observable.<Integer>error(new RuntimeException("Forced failure"));
+        
+        Observable<Integer> m = source1.join(source2, 
+                just(Observable.never()), 
+                just(duration1), add);
+        m.subscribe(observer);
+
+        source2.onNext(1);
+        
+        
+        verify(observer, times(1)).onError(any(Throwable.class));
+        verify(observer, never()).onCompleted();
+        verify(observer, never()).onNext(any());
+    }
+    @Test
+    public void leftDurationSelectorThrows() {
+        PublishSubject<Integer> source1 = PublishSubject.create();
+        PublishSubject<Integer> source2 = PublishSubject.create();
+
+        Func1<Integer, Observable<Integer>> fail = new Func1<Integer, Observable<Integer>>() {
+            @Override
+            public Observable<Integer> call(Integer t1) {
+                throw new RuntimeException("Forced failure");
+            }
+        };
+        
+        Observable<Integer> m = source1.join(source2, 
+                fail, 
+                just(Observable.never()), add);
+        m.subscribe(observer);
+
+        source1.onNext(1);
+        
+        
+        verify(observer, times(1)).onError(any(Throwable.class));
+        verify(observer, never()).onCompleted();
+        verify(observer, never()).onNext(any());
+    }
+    @Test
+    public void rightDurationSelectorThrows() {
+        PublishSubject<Integer> source1 = PublishSubject.create();
+        PublishSubject<Integer> source2 = PublishSubject.create();
+
+        Func1<Integer, Observable<Integer>> fail = new Func1<Integer, Observable<Integer>>() {
+            @Override
+            public Observable<Integer> call(Integer t1) {
+                throw new RuntimeException("Forced failure");
+            }
+        };
+        
+        Observable<Integer> m = source1.join(source2, 
+                just(Observable.never()), 
+                fail, add);
+        m.subscribe(observer);
+
+        source2.onNext(1);
+        
+        
+        verify(observer, times(1)).onError(any(Throwable.class));
+        verify(observer, never()).onCompleted();
+        verify(observer, never()).onNext(any());
+    }
+    @Test
+    public void resultSelectorThrows() {
+        PublishSubject<Integer> source1 = PublishSubject.create();
+        PublishSubject<Integer> source2 = PublishSubject.create();
+        
+        Func2<Integer, Integer, Integer> fail = new Func2<Integer, Integer, Integer>() {
+            @Override
+            public Integer call(Integer t1, Integer t2) {
+                throw new RuntimeException("Forced failure");
+            }            
+        };
+        
+        Observable<Integer> m = source1.join(source2, 
+                just(Observable.never()), 
+                just(Observable.never()), fail);
+        m.subscribe(observer);
+
+        source1.onNext(1);
+        source2.onNext(2);
+        
+        
+        verify(observer, times(1)).onError(any(Throwable.class));
+        verify(observer, never()).onCompleted();
+        verify(observer, never()).onNext(any());
+    }
+}