diff --git a/packages/react-navigation/examples/NavigationPlayground/js/SimpleStack.js b/packages/react-navigation/examples/NavigationPlayground/js/SimpleStack.js
index 3606b9ac..f392f67c 100644
--- a/packages/react-navigation/examples/NavigationPlayground/js/SimpleStack.js
+++ b/packages/react-navigation/examples/NavigationPlayground/js/SimpleStack.js
@@ -32,13 +32,8 @@ class MyNavScreen extends React.Component<MyNavScreenProps> {
           title="Go to a photos screen"
         />
         <Button
-          onPress={() =>
-            navigation.navigate('Profile', {
-              name: 'Dog',
-              headerBackImage: require('./assets/dog-back.png'),
-            })
-          }
-          title="Custom back button"
+          onPress={() => navigation.replace('Profile', { name: 'Lucy' })}
+          title="Replace with profile"
         />
         <Button onPress={() => navigation.goBack(null)} title="Go back" />
         <StatusBar barStyle="default" />
diff --git a/packages/react-navigation/flow/react-navigation.js b/packages/react-navigation/flow/react-navigation.js
index ae74966b..a0cbace0 100644
--- a/packages/react-navigation/flow/react-navigation.js
+++ b/packages/react-navigation/flow/react-navigation.js
@@ -1,7 +1,6 @@
 // @flow
 
 declare module 'react-navigation' {
-
   /**
    * First, a bunch of things we would love to import but instead must
    * reconstruct (mostly copy-pasted).
@@ -68,6 +67,8 @@ declare module 'react-navigation' {
 
     // The action to run inside the sub-router
     action?: NavigationNavigateAction,
+
+    key?: string,
   |};
 
   declare type DeprecatedNavigationNavigateAction = {|
@@ -130,8 +131,9 @@ declare module 'react-navigation' {
     type: 'Reset',
     index: number,
     key?: ?string,
-    actions:
-      Array<NavigationNavigateAction | DeprecatedNavigationNavigateAction>,
+    actions: Array<
+      NavigationNavigateAction | DeprecatedNavigationNavigateAction
+    >,
   |};
 
   declare export type NavigationUriAction = {|
@@ -144,9 +146,37 @@ declare module 'react-navigation' {
     uri: string,
   |};
 
+  declare export type NavigationReplaceAction = {|
+    +type: 'Navigation/REPLACE',
+    +key: string,
+    +routeName: string,
+    +params?: NavigationParams,
+    +action?: NavigationNavigateAction,
+  |};
+  declare export type NavigationPopAction = {|
+    +type: 'Navigation/POP',
+    +n?: number,
+    +immediate?: boolean,
+  |};
+  declare export type NavigationPopToTopAction = {|
+    +type: 'Navigation/POP_TO_TOP',
+    +immediate?: boolean,
+  |};
+  declare export type NavigationPushAction = {|
+    +type: 'Navigation/PUSH',
+    +routeName: string,
+    +params?: NavigationParams,
+    +action?: NavigationNavigateAction,
+    +key?: string,
+  |};
+
   declare export type NavigationAction =
     | NavigationInitAction
     | NavigationNavigateAction
+    | NavigationReplaceAction
+    | NavigationPopAction
+    | NavigationPopToTopAction
+    | NavigationPushAction
     | NavigationBackAction
     | NavigationSetParamsAction
     | NavigationResetAction;
@@ -209,9 +239,8 @@ declare module 'react-navigation' {
     params?: NavigationParams,
   };
 
-  declare export type NavigationStateRoute =
-    & NavigationLeafRoute
-    & NavigationState;
+  declare export type NavigationStateRoute = NavigationLeafRoute &
+    NavigationState;
 
   /**
    * Router
@@ -291,12 +320,8 @@ declare module 'react-navigation' {
     Route: NavigationRoute,
     Options: {},
     Props: {}
-  > =
-    & React$ComponentType<NavigationNavigatorProps<Options, Route> & Props>
-    & (
-        | {}
-        | { navigationOptions: NavigationScreenConfig<Options> }
-      );
+  > = React$ComponentType<NavigationNavigatorProps<Options, Route> & Props> &
+    ({} | { navigationOptions: NavigationScreenConfig<Options> });
 
   declare export type NavigationNavigator<
     State: NavigationState,
@@ -334,16 +359,18 @@ declare module 'react-navigation' {
 
   declare export type HeaderMode = 'float' | 'screen' | 'none';
 
-  declare export type HeaderProps = $Shape<NavigationSceneRendererProps & {
-    mode: HeaderMode,
-    router: NavigationRouter<NavigationState, NavigationStackScreenOptions>,
-    getScreenDetails: NavigationScene => NavigationScreenDetails<
-      NavigationStackScreenOptions
-    >,
-    leftInterpolator: (props: NavigationSceneRendererProps) => {},
-    titleInterpolator: (props: NavigationSceneRendererProps) => {},
-    rightInterpolator: (props: NavigationSceneRendererProps) => {},
-  }>;
+  declare export type HeaderProps = $Shape<
+    NavigationSceneRendererProps & {
+      mode: HeaderMode,
+      router: NavigationRouter<NavigationState, NavigationStackScreenOptions>,
+      getScreenDetails: NavigationScene => NavigationScreenDetails<
+        NavigationStackScreenOptions
+      >,
+      leftInterpolator: (props: NavigationSceneRendererProps) => {},
+      titleInterpolator: (props: NavigationSceneRendererProps) => {},
+      rightInterpolator: (props: NavigationSceneRendererProps) => {},
+    }
+  >;
 
   /**
    * Stack Navigator
@@ -493,6 +520,18 @@ declare module 'react-navigation' {
       eventName: string,
       callback: NavigationEventCallback
     ) => NavigationEventSubscription,
+    push: (
+      routeName: string,
+      params?: NavigationParams,
+      action?: NavigationNavigateAction
+    ) => boolean,
+    replace: (
+      routeName: string,
+      params?: NavigationParams,
+      action?: NavigationNavigateAction
+    ) => boolean,
+    pop: (n?: number, params?: { immediate?: boolean }) => boolean,
+    popToTop: (params?: { immediate?: boolean }) => boolean,
   };
 
   declare export type NavigationNavigatorProps<O: {}, S: {}> = $Shape<{
@@ -767,7 +806,7 @@ declare module 'react-navigation' {
   >(
     router: NavigationRouter<S, O>,
     routeConfigs?: NavigationRouteConfigMap,
-    navigatorConfig?: NavigatorConfig,
+    navigatorConfig?: NavigatorConfig
   ): _NavigatorCreator<NavigationViewProps, S, O>;
 
   declare export function StackNavigator(
diff --git a/packages/react-navigation/src/NavigationActions.js b/packages/react-navigation/src/NavigationActions.js
index 453c46f2..8f4fbd15 100644
--- a/packages/react-navigation/src/NavigationActions.js
+++ b/packages/react-navigation/src/NavigationActions.js
@@ -5,6 +5,7 @@ const POP = 'Navigation/POP';
 const POP_TO_TOP = 'Navigation/POP_TO_TOP';
 const PUSH = 'Navigation/PUSH';
 const RESET = 'Navigation/RESET';
+const REPLACE = 'Navigation/REPLACE';
 const SET_PARAMS = 'Navigation/SET_PARAMS';
 const URI = 'Navigation/URI';
 const COMPLETE_TRANSITION = 'Navigation/COMPLETE_TRANSITION';
@@ -79,6 +80,15 @@ const reset = createAction(RESET, payload => ({
   actions: payload.actions,
 }));
 
+const replace = createAction(REPLACE, payload => ({
+  type: REPLACE,
+  key: payload.key,
+  params: payload.params,
+  action: payload.action,
+  routeName: payload.routeName,
+  immediate: payload.immediate,
+}));
+
 const setParams = createAction(SET_PARAMS, payload => ({
   type: SET_PARAMS,
   key: payload.key,
@@ -157,6 +167,7 @@ export default {
   POP_TO_TOP,
   PUSH,
   RESET,
+  REPLACE,
   SET_PARAMS,
   URI,
   COMPLETE_TRANSITION,
@@ -169,6 +180,7 @@ export default {
   popToTop,
   push,
   reset,
+  replace,
   setParams,
   uri,
   completeTransition,
diff --git a/packages/react-navigation/src/addNavigationHelpers.js b/packages/react-navigation/src/addNavigationHelpers.js
index 0841ce92..a56721cf 100644
--- a/packages/react-navigation/src/addNavigationHelpers.js
+++ b/packages/react-navigation/src/addNavigationHelpers.js
@@ -65,5 +65,15 @@ export default function(navigation) {
       navigation.dispatch(
         NavigationActions.push({ routeName, params, action })
       ),
+
+    replace: (routeName, params, action) =>
+      navigation.dispatch(
+        NavigationActions.replace({
+          routeName,
+          params,
+          action,
+          key: navigation.state.key,
+        })
+      ),
   };
 }
diff --git a/packages/react-navigation/src/navigators/__tests__/__snapshots__/StackNavigator-test.js.snap b/packages/react-navigation/src/navigators/__tests__/__snapshots__/StackNavigator-test.js.snap
index 41e4687f..90e7a5d0 100644
--- a/packages/react-navigation/src/navigators/__tests__/__snapshots__/StackNavigator-test.js.snap
+++ b/packages/react-navigation/src/navigators/__tests__/__snapshots__/StackNavigator-test.js.snap
@@ -100,6 +100,7 @@ exports[`StackNavigator applies correct values when headerRight is present 1`] =
           "pop": [Function],
           "popToTop": [Function],
           "push": [Function],
+          "replace": [Function],
           "setParams": [Function],
           "state": Object {
             "index": 0,
@@ -337,6 +338,7 @@ exports[`StackNavigator renders successfully 1`] = `
           "pop": [Function],
           "popToTop": [Function],
           "push": [Function],
+          "replace": [Function],
           "setParams": [Function],
           "state": Object {
             "index": 0,
diff --git a/packages/react-navigation/src/routers/StackRouter.js b/packages/react-navigation/src/routers/StackRouter.js
index f8093a0a..fb3cea5a 100644
--- a/packages/react-navigation/src/routers/StackRouter.js
+++ b/packages/react-navigation/src/routers/StackRouter.js
@@ -171,7 +171,7 @@ export default (routeConfigs, stackConfig = {}) => {
         }
       }
 
-      //Handle pop-to-top behavior. Make sure this happens after children have had a chance to handle the action, so that the inner stack pops to top first.
+      // Handle pop-to-top behavior. Make sure this happens after children have had a chance to handle the action, so that the inner stack pops to top first.
       if (action.type === NavigationActions.POP_TO_TOP) {
         if (state.index !== 0) {
           return {
@@ -183,6 +183,31 @@ export default (routeConfigs, stackConfig = {}) => {
         return state;
       }
 
+      // Handle replace action
+      if (action.type === NavigationActions.REPLACE) {
+        const routeIndex = state.routes.findIndex(r => r.key === action.key);
+        // Only replace if the key matches one of our routes
+        if (routeIndex !== -1) {
+          const childRouter = childRouters[action.routeName];
+          let childState = {};
+          if (childRouter) {
+            const childAction =
+              action.action ||
+              NavigationActions.init({ params: action.params });
+            childState = childRouter.getStateForAction(childAction);
+          }
+          const routes = [...state.routes];
+          routes[routeIndex] = {
+            params: action.params,
+            // merge the child state in this order to allow params override
+            ...childState,
+            key: action.key,
+            routeName: action.routeName,
+          };
+          return { ...state, routes };
+        }
+      }
+
       // Handle explicit push navigation action. Make sure this happens after children have had a chance to handle the action
       if (
         behavesLikePushAction(action) &&
@@ -235,6 +260,7 @@ export default (routeConfigs, stackConfig = {}) => {
             action.action || NavigationActions.init({ params: action.params });
           route = {
             params: action.params,
+            // merge the child state in this order to allow params override
             ...childRouter.getStateForAction(childAction),
             key,
             routeName: action.routeName,
diff --git a/packages/react-navigation/src/routers/__tests__/StackRouter-test.js b/packages/react-navigation/src/routers/__tests__/StackRouter-test.js
index e7b9c727..2697b7b4 100644
--- a/packages/react-navigation/src/routers/__tests__/StackRouter-test.js
+++ b/packages/react-navigation/src/routers/__tests__/StackRouter-test.js
@@ -515,6 +515,28 @@ describe('StackRouter', () => {
     });
   });
 
+  test('Replace action works', () => {
+    const TestRouter = StackRouter({
+      foo: { screen: () => <div /> },
+      bar: { screen: () => <div /> },
+    });
+    const initState = TestRouter.getStateForAction(
+      NavigationActions.navigate({ routeName: 'foo' })
+    );
+    const replacedState = TestRouter.getStateForAction(
+      NavigationActions.replace({
+        routeName: 'bar',
+        params: { meaning: 42 },
+        key: initState.routes[0].key,
+      }),
+      initState
+    );
+    expect(replacedState.index).toEqual(0);
+    expect(replacedState.routes.length).toEqual(1);
+    expect(replacedState.routes[0].routeName).toEqual('bar');
+    expect(replacedState.routes[0].params.meaning).toEqual(42);
+  });
+
   test('Handles push transition logic with completion action', () => {
     const FooScreen = () => <div />;
     const BarScreen = () => <div />;
diff --git a/packages/react-navigation/src/views/__tests__/__snapshots__/TabView-test.js.snap b/packages/react-navigation/src/views/__tests__/__snapshots__/TabView-test.js.snap
index 904069ec..ecf9a47c 100644
--- a/packages/react-navigation/src/views/__tests__/__snapshots__/TabView-test.js.snap
+++ b/packages/react-navigation/src/views/__tests__/__snapshots__/TabView-test.js.snap
@@ -240,6 +240,7 @@ exports[`TabBarBottom renders successfully 1`] = `
                 "pop": [Function],
                 "popToTop": [Function],
                 "push": [Function],
+                "replace": [Function],
                 "setParams": [Function],
                 "state": Object {
                   "key": "s1",