diff --git a/Libraries/Components/ActivityIndicatorIOS/ActivityIndicatorIOS.ios.js b/Libraries/Components/ActivityIndicatorIOS/ActivityIndicatorIOS.ios.js
index b673258722..f2bcbfd516 100644
--- a/Libraries/Components/ActivityIndicatorIOS/ActivityIndicatorIOS.ios.js
+++ b/Libraries/Components/ActivityIndicatorIOS/ActivityIndicatorIOS.ios.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ActivityIndicatorIOS
+ * @flow
  */
 'use strict';
 
@@ -29,6 +30,12 @@ var SpinnerSize = keyMirror({
 
 var GRAY = '#999999';
 
+type DefaultProps = {
+  animating: boolean;
+  size: 'small' | 'large';
+  color: string;
+};
+
 var ActivityIndicatorIOS = React.createClass({
   mixins: [NativeMethodsMixin],
 
@@ -51,7 +58,7 @@ var ActivityIndicatorIOS = React.createClass({
     ]),
   },
 
-  getDefaultProps: function() {
+  getDefaultProps: function(): DefaultProps {
     return {
       animating: true,
       size: SpinnerSize.small,
diff --git a/Libraries/Components/DatePicker/DatePickerIOS.ios.js b/Libraries/Components/DatePicker/DatePickerIOS.ios.js
index 7be126675d..9bd0a2ac47 100644
--- a/Libraries/Components/DatePicker/DatePickerIOS.ios.js
+++ b/Libraries/Components/DatePicker/DatePickerIOS.ios.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule DatePickerIOS
+ * @flow
  *
  * This is a controlled component version of RCTDatePickerIOS
  */
@@ -26,6 +27,12 @@ var merge = require('merge');
 
 var DATEPICKER = 'datepicker';
 
+type DefaultProps = {
+  mode: 'date' | 'time' | 'datetime';
+};
+
+type Event = Object;
+
 /**
  * Use `DatePickerIOS` to render a date/time picker (selector) on iOS.  This is
  * a controlled component, so you must hook in to the `onDateChange` callback
@@ -85,13 +92,13 @@ var DatePickerIOS = React.createClass({
     timeZoneOffsetInMinutes: PropTypes.number,
   },
 
-  getDefaultProps: function() {
+  getDefaultProps: function(): DefaultProps {
     return {
       mode: 'datetime',
     };
   },
 
-  _onChange: function(event) {
+  _onChange: function(event: Event) {
     var nativeTimeStamp = event.nativeEvent.timestamp;
     this.props.onDateChange && this.props.onDateChange(
       new Date(nativeTimeStamp)
diff --git a/Libraries/Components/MapView/MapView.js b/Libraries/Components/MapView/MapView.js
index b2409a05b9..b778fc695b 100644
--- a/Libraries/Components/MapView/MapView.js
+++ b/Libraries/Components/MapView/MapView.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule MapView
+ * @flow
  */
 'use strict';
 
@@ -21,6 +22,8 @@ var deepDiffer = require('deepDiffer');
 var insetsDiffer = require('insetsDiffer');
 var merge = require('merge');
 
+type Event = Object;
+
 var MapView = React.createClass({
   mixins: [NativeMethodsMixin],
 
@@ -119,7 +122,7 @@ var MapView = React.createClass({
     onRegionChangeComplete: React.PropTypes.func,
   },
 
-  _onChange: function(event) {
+  _onChange: function(event: Event) {
     if (event.nativeEvent.continuous) {
       this.props.onRegionChange &&
         this.props.onRegionChange(event.nativeEvent.region);
diff --git a/Libraries/Components/Navigation/NavigatorIOS.ios.js b/Libraries/Components/Navigation/NavigatorIOS.ios.js
index 06c353592d..aa5039edbf 100644
--- a/Libraries/Components/Navigation/NavigatorIOS.ios.js
+++ b/Libraries/Components/Navigation/NavigatorIOS.ios.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule NavigatorIOS
+ * @flow
  */
 'use strict';
 
@@ -59,7 +60,7 @@ var RCTNavigatorItem = createReactIOSNativeComponentClass({
 var NavigatorTransitionerIOS = React.createClass({
   requestSchedulingNavigation: function(cb) {
     RCTNavigatorManager.requestSchedulingJavaScriptNavigation(
-      this.getNodeHandle(),
+      (this: any).getNodeHandle(),
       logError,
       cb
     );
@@ -72,6 +73,29 @@ var NavigatorTransitionerIOS = React.createClass({
   },
 });
 
+type Route = {
+  component: Function;
+  title: string;
+  passProps: Object;
+  backButtonTitle: string;
+  rightButtonTitle: string;
+  onRightButtonPress: Function;
+  wrapperStyle: any;
+};
+
+type State = {
+  idStack: Array<number>;
+  routeStack: Array<Route>;
+  requestedTopOfStack: number;
+  observedTopOfStack: number;
+  progress: number;
+  fromIndex: number;
+  toIndex: number;
+  makingNavigatorRequest: boolean;
+  updatingAllIndicesAtOrBeyond: number;
+}
+
+type Event = Object;
 
 /**
  * Think of `<NavigatorIOS>` as simply a component that renders an
@@ -224,6 +248,8 @@ var NavigatorIOS = React.createClass({
 
   },
 
+  navigator: (undefined: ?Object),
+
   componentWillMount: function() {
     // Precompute a pack of callbacks that's frequently generated and passed to
     // instances.
@@ -240,7 +266,7 @@ var NavigatorIOS = React.createClass({
     };
   },
 
-  getInitialState: function() {
+  getInitialState: function(): State {
     return {
       idStack: [getuid()],
       routeStack: [this.props.initialRoute],
@@ -266,7 +292,9 @@ var NavigatorIOS = React.createClass({
     };
   },
 
-  _handleFocusRequest: function(item) {
+  _toFocusOnNavigationComplete: (undefined: any),
+
+  _handleFocusRequest: function(item: any) {
     if (this.state.makingNavigatorRequest) {
       this._toFocusOnNavigationComplete = item;
     } else {
@@ -274,14 +302,22 @@ var NavigatorIOS = React.createClass({
     }
   },
 
-  _getFocusEmitter: function() {
-    if (!this._focusEmitter) {
-      this._focusEmitter = new EventEmitter();
+  _focusEmitter: (undefined: ?EventEmitter),
+
+  _getFocusEmitter: function(): EventEmitter {
+    // Flow not yet tracking assignments to instance fields.
+    var focusEmitter = this._focusEmitter;
+    if (!focusEmitter) {
+      focusEmitter = new EventEmitter();
+      this._focusEmitter = focusEmitter;
     }
-    return this._focusEmitter;
+    return focusEmitter;
   },
 
-  getChildContext: function() {
+  getChildContext: function(): {
+    onFocusRequested: Function;
+    focusEmitter: EventEmitter;
+  } {
     return {
       onFocusRequested: this._handleFocusRequest,
       focusEmitter: this._getFocusEmitter(),
@@ -293,13 +329,13 @@ var NavigatorIOS = React.createClass({
     focusEmitter: React.PropTypes.instanceOf(EventEmitter),
   },
 
-  _tryLockNavigator: function(cb) {
+  _tryLockNavigator: function(cb: () => void) {
     this.refs[TRANSITIONER_REF].requestSchedulingNavigation(
       (acquiredLock) => acquiredLock && cb()
     );
   },
 
-  _handleNavigatorStackChanged: function(e) {
+  _handleNavigatorStackChanged: function(e: Event) {
     var newObservedTopOfStack = e.nativeEvent.stackLength - 1;
     invariant(
       newObservedTopOfStack <= this.state.requestedTopOfStack,
@@ -352,7 +388,7 @@ var NavigatorIOS = React.createClass({
     });
   },
 
-  push: function(route) {
+  push: function(route: Route) {
     invariant(!!route, 'Must supply route to push');
     // Make sure all previous requests are caught up first. Otherwise reject.
     if (this.state.requestedTopOfStack === this.state.observedTopOfStack) {
@@ -372,7 +408,7 @@ var NavigatorIOS = React.createClass({
     }
   },
 
-  popN: function(n) {
+  popN: function(n: number) {
     if (n === 0) {
       return;
     }
@@ -406,7 +442,7 @@ var NavigatorIOS = React.createClass({
    * `index` specifies the route in the stack that should be replaced.
    * If it's negative, it counts from the back.
    */
-  replaceAtIndex: function(route, index) {
+  replaceAtIndex: function(route: Route, index: number) {
     invariant(!!route, 'Must supply route to replace');
     if (index < 0) {
       index += this.state.routeStack.length;
@@ -434,14 +470,14 @@ var NavigatorIOS = React.createClass({
   /**
    * Replaces the top of the navigation stack.
    */
-  replace: function(route) {
+  replace: function(route: Route) {
     this.replaceAtIndex(route, -1);
   },
 
   /**
    * Replace the current route's parent.
    */
-  replacePrevious: function(route) {
+  replacePrevious: function(route: Route) {
     this.replaceAtIndex(route, -2);
   },
 
@@ -449,7 +485,7 @@ var NavigatorIOS = React.createClass({
     this.popToRoute(this.state.routeStack[0]);
   },
 
-  popToRoute: function(route) {
+  popToRoute: function(route: Route) {
     var indexOfRoute = this.state.routeStack.indexOf(route);
     invariant(
       indexOfRoute !== -1,
@@ -459,7 +495,7 @@ var NavigatorIOS = React.createClass({
     this.popN(numToPop);
   },
 
-  replacePreviousAndPop: function(route) {
+  replacePreviousAndPop: function(route: Route) {
     // Make sure all previous requests are caught up first. Otherwise reject.
     if (this.state.requestedTopOfStack !== this.state.observedTopOfStack) {
       return;
@@ -476,7 +512,7 @@ var NavigatorIOS = React.createClass({
     });
   },
 
-  resetTo: function(route) {
+  resetTo: function(route: Route) {
     invariant(!!route, 'Must supply route to push');
     // Make sure all previous requests are caught up first. Otherwise reject.
     if (this.state.requestedTopOfStack !== this.state.observedTopOfStack) {
@@ -486,7 +522,7 @@ var NavigatorIOS = React.createClass({
     this.popToRoute(route);
   },
 
-  handleNavigationComplete: function(e) {
+  handleNavigationComplete: function(e: Event) {
     if (this._toFocusOnNavigationComplete) {
       this._getFocusEmitter().emit('focus', this._toFocusOnNavigationComplete);
       this._toFocusOnNavigationComplete = null;
@@ -494,7 +530,7 @@ var NavigatorIOS = React.createClass({
     this._handleNavigatorStackChanged(e);
   },
 
-  _routeToStackItem: function(route, i) {
+  _routeToStackItem: function(route: Route, i: number) {
     var Component = route.component;
     var shouldUpdateChild = this.state.updatingAllIndicesAtOrBeyond !== null &&
       this.state.updatingAllIndicesAtOrBeyond >= i;
diff --git a/Libraries/Components/ScrollResponder.js b/Libraries/Components/ScrollResponder.js
index 471487cd10..c9756908a5 100644
--- a/Libraries/Components/ScrollResponder.js
+++ b/Libraries/Components/ScrollResponder.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ScrollResponder
+ * @flow
  */
 'use strict';
 
@@ -102,10 +103,19 @@ var warning = require('warning');
 
 var IS_ANIMATING_TOUCH_START_THRESHOLD_MS = 16;
 
+type State = {
+    isTouching: boolean;
+    lastMomentumScrollBeginTime: number;
+    lastMomentumScrollEndTime: number;
+    observedScrollSinceBecomingResponder: boolean;
+    becameResponderWhileAnimating: boolean;
+};
+type Event = Object;
+
 var ScrollResponderMixin = {
   mixins: [Subscribable.Mixin],
   statics: RCTScrollViewConsts,
-  scrollResponderMixinGetInitialState: function() {
+  scrollResponderMixinGetInitialState: function(): State {
     return {
       isTouching: false,
       lastMomentumScrollBeginTime: 0,
@@ -124,7 +134,7 @@ var ScrollResponderMixin = {
   /**
    * Invoke this from an `onScroll` event.
    */
-  scrollResponderHandleScrollShouldSetResponder: function() {
+  scrollResponderHandleScrollShouldSetResponder: function(): boolean {
     return this.state.isTouching;
   },
 
@@ -153,7 +163,7 @@ var ScrollResponderMixin = {
    *   true.
    *
    */
-  scrollResponderHandleStartShouldSetResponder: function() {
+  scrollResponderHandleStartShouldSetResponder: function(): boolean {
     return false;
   },
 
@@ -168,7 +178,7 @@ var ScrollResponderMixin = {
    *
    * Invoke this from an `onStartShouldSetResponderCapture` event.
    */
-  scrollResponderHandleStartShouldSetResponderCapture: function(e) {
+  scrollResponderHandleStartShouldSetResponderCapture: function(e: Event): boolean {
     // First see if we want to eat taps while the keyboard is up
     var currentlyFocusedTextInput = TextInputState.currentlyFocusedField();
     if (!this.props.keyboardShouldPersistTaps &&
@@ -208,7 +218,7 @@ var ScrollResponderMixin = {
    *   navigation of a swipe gesture higher in the view hierarchy, should be
    *   rejected.
    */
-  scrollResponderHandleTerminationRequest: function() {
+  scrollResponderHandleTerminationRequest: function(): boolean {
     return !this.state.observedScrollSinceBecomingResponder;
   },
 
@@ -217,7 +227,7 @@ var ScrollResponderMixin = {
    *
    * @param {SyntheticEvent} e Event.
    */
-  scrollResponderHandleTouchEnd: function(e) {
+  scrollResponderHandleTouchEnd: function(e: Event) {
     var nativeEvent = e.nativeEvent;
     this.state.isTouching = nativeEvent.touches.length !== 0;
     this.props.onTouchEnd && this.props.onTouchEnd(e);
@@ -226,7 +236,7 @@ var ScrollResponderMixin = {
   /**
    * Invoke this from an `onResponderRelease` event.
    */
-  scrollResponderHandleResponderRelease: function(e) {
+  scrollResponderHandleResponderRelease: function(e: Event) {
     this.props.onResponderRelease && this.props.onResponderRelease(e);
 
     // By default scroll views will unfocus a textField
@@ -243,7 +253,7 @@ var ScrollResponderMixin = {
     }
   },
 
-  scrollResponderHandleScroll: function(e) {
+  scrollResponderHandleScroll: function(e: Event) {
     this.state.observedScrollSinceBecomingResponder = true;
     this.props.onScroll && this.props.onScroll(e);
   },
@@ -251,7 +261,7 @@ var ScrollResponderMixin = {
   /**
    * Invoke this from an `onResponderGrant` event.
    */
-  scrollResponderHandleResponderGrant: function(e) {
+  scrollResponderHandleResponderGrant: function(e: Event) {
     this.state.observedScrollSinceBecomingResponder = false;
     this.props.onResponderGrant && this.props.onResponderGrant(e);
     this.state.becameResponderWhileAnimating = this.scrollResponderIsAnimating();
@@ -264,21 +274,21 @@ var ScrollResponderMixin = {
    *
    * Invoke this from an `onScrollBeginDrag` event.
    */
-  scrollResponderHandleScrollBeginDrag: function(e) {
+  scrollResponderHandleScrollBeginDrag: function(e: Event) {
     this.props.onScrollBeginDrag && this.props.onScrollBeginDrag(e);
   },
 
   /**
    * Invoke this from an `onScrollEndDrag` event.
    */
-  scrollResponderHandleScrollEndDrag: function(e) {
+  scrollResponderHandleScrollEndDrag: function(e: Event) {
     this.props.onScrollEndDrag && this.props.onScrollEndDrag(e);
   },
 
   /**
    * Invoke this from an `onMomentumScrollBegin` event.
    */
-  scrollResponderHandleMomentumScrollBegin: function(e) {
+  scrollResponderHandleMomentumScrollBegin: function(e: Event) {
     this.state.lastMomentumScrollBeginTime = Date.now();
     this.props.onMomentumScrollBegin && this.props.onMomentumScrollBegin(e);
   },
@@ -286,7 +296,7 @@ var ScrollResponderMixin = {
   /**
    * Invoke this from an `onMomentumScrollEnd` event.
    */
-  scrollResponderHandleMomentumScrollEnd: function(e) {
+  scrollResponderHandleMomentumScrollEnd: function(e: Event) {
     this.state.lastMomentumScrollEndTime = Date.now();
     this.props.onMomentumScrollEnd && this.props.onMomentumScrollEnd(e);
   },
@@ -302,7 +312,7 @@ var ScrollResponderMixin = {
    *
    * @param {SyntheticEvent} e Touch Start event.
    */
-  scrollResponderHandleTouchStart: function(e) {
+  scrollResponderHandleTouchStart: function(e: Event) {
     this.state.isTouching = true;
     this.props.onTouchStart && this.props.onTouchStart(e);
   },
@@ -318,7 +328,7 @@ var ScrollResponderMixin = {
    *
    * @param {SyntheticEvent} e Touch Start event.
    */
-  scrollResponderHandleTouchMove: function(e) {
+  scrollResponderHandleTouchMove: function(e: Event) {
     this.props.onTouchMove && this.props.onTouchMove(e);
   },
 
@@ -327,7 +337,7 @@ var ScrollResponderMixin = {
    * view is currently animating. This is particularly useful to know when
    * a touch has just started or ended.
    */
-  scrollResponderIsAnimating: function() {
+  scrollResponderIsAnimating: function(): boolean {
     var now = Date.now();
     var timeSinceLastMomentumScrollEnd = now - this.state.lastMomentumScrollEndTime;
     var isAnimating = timeSinceLastMomentumScrollEnd < IS_ANIMATING_TOUCH_START_THRESHOLD_MS ||
@@ -340,7 +350,7 @@ var ScrollResponderMixin = {
    * This is currently used to help focus on child textview's, but this
    * can also be used to quickly scroll to any element we want to focus
    */
-  scrollResponderScrollTo: function(offsetX, offsetY) {
+  scrollResponderScrollTo: function(offsetX: number, offsetY: number) {
     RCTUIManagerDeprecated.scrollTo(this.getNodeHandle(), offsetX, offsetY);
   },
 
@@ -348,7 +358,7 @@ var ScrollResponderMixin = {
    * A helper function to zoom to a specific rect in the scrollview.
    * @param {object} rect Should have shape {x, y, w, h}
    */
-  scrollResponderZoomTo: function(rect) {
+  scrollResponderZoomTo: function(rect: { x: number; y: number; w: number; h: number; }) {
     RCTUIManagerDeprecated.zoomToRect(this.getNodeHandle(), rect);
   },
 
@@ -357,7 +367,7 @@ var ScrollResponderMixin = {
    * parent view. Note that any module using this mixin needs to return
    * the parent view's ref in getScrollViewRef() in order to use this method
    */
-  scrollResponderScrollNativeHandleToKeyboard: function(nodeHandle, additionalOffset) {
+    scrollResponderScrollNativeHandleToKeyboard: function(nodeHandle: any, additionalOffset?: number) {
     this.additionalScrollOffset = additionalOffset || 0;
     RCTUIManager.measureLayout(
       nodeHandle,
@@ -377,7 +387,7 @@ var ScrollResponderMixin = {
    * @param {number} width Width of the text input.
    * @param {number} height Height of the text input.
    */
-  scrollResponderInputMeasureAndScrollToKeyboard: function(left, top, width, height) {
+    scrollResponderInputMeasureAndScrollToKeyboard: function(left: number, top: number, width: number, height: number) {
     if (this.keyboardWillOpenTo) {
       var scrollOffsetY =
         top - this.keyboardWillOpenTo.endCoordinates.screenY + height +
@@ -387,7 +397,7 @@ var ScrollResponderMixin = {
     this.additionalOffset = 0;
   },
 
-  scrollResponderTextInputFocusError: function(e) {
+  scrollResponderTextInputFocusError: function(e: Event) {
     console.error('Error measuring text field: ', e);
   },
 
@@ -434,12 +444,12 @@ var ScrollResponderMixin = {
    * relevant to you. (For example, only if you receive these callbacks after
    * you had explicitly focused a node etc).
    */
-  scrollResponderKeyboardWillShow: function(e) {
+  scrollResponderKeyboardWillShow: function(e: Event) {
     this.keyboardWillOpenTo = e;
     this.props.onKeyboardWillShow && this.props.onKeyboardWillShow(e);
   },
 
-  scrollResponderKeyboardWillHide: function(e) {
+  scrollResponderKeyboardWillHide: function(e: Event) {
     this.keyboardWillOpenTo = null;
     this.props.onKeyboardWillHide && this.props.onKeyboardWillHide(e);
   },
diff --git a/Libraries/Components/ScrollView/ScrollView.js b/Libraries/Components/ScrollView/ScrollView.js
index 5f4e8700d1..92cdab05ac 100644
--- a/Libraries/Components/ScrollView/ScrollView.js
+++ b/Libraries/Components/ScrollView/ScrollView.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ScrollView
+ * @flow
  */
 'use strict';
 
@@ -178,15 +179,15 @@ var ScrollView = React.createClass({
     return this.scrollResponderMixinGetInitialState();
   },
 
-  setNativeProps: function(props) {
+  setNativeProps: function(props: Object) {
     this.refs[SCROLLVIEW].setNativeProps(props);
   },
 
-  getInnerViewNode: function() {
+  getInnerViewNode: function(): any {
     return this.refs[INNERVIEW].getNodeHandle();
   },
 
-  scrollTo: function(destY, destX) {
+  scrollTo: function(destY?: number, destX?: number) {
     RCTUIManager.scrollTo(
       this.getNodeHandle(),
       destX || 0,
@@ -202,7 +203,7 @@ var ScrollView = React.createClass({
     if (__DEV__ && this.props.style) {
       var style = flattenStyle(this.props.style);
       var childLayoutProps = ['alignItems', 'justifyContent']
-        .filter((prop) => style[prop] !== undefined);
+        .filter((prop) => style && style[prop] !== undefined);
       invariant(
         childLayoutProps.length === 0,
         'ScrollView child layout (' + JSON.stringify(childLayoutProps) +
@@ -250,7 +251,7 @@ var ScrollView = React.createClass({
       keyboardDismissMode: this.props.keyboardDismissMode ?
         keyboardDismissModeConstants[this.props.keyboardDismissMode] :
         undefined,
-      style: [styles.base, this.props.style],
+      style: ([styles.base, this.props.style]: ?Array<any>),
       onTouchStart: this.scrollResponderHandleTouchStart,
       onTouchMove: this.scrollResponderHandleTouchMove,
       onTouchEnd: this.scrollResponderHandleTouchEnd,
@@ -279,6 +280,10 @@ var ScrollView = React.createClass({
         ScrollViewClass = AndroidScrollView;
       }
     }
+    invariant(
+      ScrollViewClass !== undefined,
+      'ScrollViewClass must not be undefined'
+    );
 
     return (
       <ScrollViewClass {...props} ref={SCROLLVIEW}>
diff --git a/Libraries/Components/SliderIOS/SliderIOS.js b/Libraries/Components/SliderIOS/SliderIOS.js
index 97c848dcce..aac9798d3c 100644
--- a/Libraries/Components/SliderIOS/SliderIOS.js
+++ b/Libraries/Components/SliderIOS/SliderIOS.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule SliderIOS
+ * @flow
  */
 'use strict';
 
@@ -21,6 +22,8 @@ var createReactIOSNativeComponentClass =
   require('createReactIOSNativeComponentClass');
 var merge = require('merge');
 
+type Event = Object;
+
 var SliderIOS = React.createClass({
   mixins: [NativeMethodsMixin],
 
@@ -52,7 +55,7 @@ var SliderIOS = React.createClass({
     onSlidingComplete: PropTypes.func,
   },
 
-  _onValueChange: function(event) {
+  _onValueChange: function(event: Event) {
     this.props.onChange && this.props.onChange(event);
     if (event.nativeEvent.continuous) {
       this.props.onValueChange &&
diff --git a/Libraries/Components/StaticRenderer.js b/Libraries/Components/StaticRenderer.js
index 0986fc64f7..8800198a5d 100644
--- a/Libraries/Components/StaticRenderer.js
+++ b/Libraries/Components/StaticRenderer.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @provides StaticRenderer
+ * @flow
  */
 'use strict';
 
@@ -18,11 +19,11 @@ var StaticRenderer = React.createClass({
     render: React.PropTypes.func.isRequired,
   },
 
-  shouldComponentUpdate: function(nextProps) {
+  shouldComponentUpdate: function(nextProps: { shouldUpdate: boolean }): boolean {
     return nextProps.shouldUpdate;
   },
 
-  render: function() {
+  render: function(): ReactElement {
     return this.props.render();
   },
 });
diff --git a/Libraries/Components/Subscribable.js b/Libraries/Components/Subscribable.js
index 797aabf297..06b7e0ce4b 100644
--- a/Libraries/Components/Subscribable.js
+++ b/Libraries/Components/Subscribable.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule Subscribable
+ * @flow
  */
 'use strict';
 
@@ -73,8 +74,13 @@ var logError = require('logError');
 
 var SUBSCRIBABLE_INTERNAL_EVENT = 'subscriptionEvent';
 
+type Data = Object;
+type EventMapping = (_: Data) => Data;
 
 class Subscribable {
+  _eventMapping: EventMapping;
+  _lastData: Data;
+
   /**
    * Creates a new Subscribable object
    *
@@ -88,7 +94,7 @@ class Subscribable {
    *   The resolved data will be transformed with the eventMapping before it
    *   gets emitted.
    */
-  constructor(eventEmitter, eventName, eventMapping, getInitData) {
+  constructor(eventEmitter: EventEmitter, eventName: string, eventMapping?: EventMapping, getInitData?: Function) {
 
     this._internalEmitter = new EventEmitter();
     this._eventMapping = eventMapping || (data => data);
@@ -106,7 +112,7 @@ class Subscribable {
   /**
    * Returns the last data emitted from the Subscribable, or undefined
    */
-  get() {
+  get(): Data {
     return this._lastData;
   }
 
@@ -138,7 +144,7 @@ class Subscribable {
    *   }
    *   Call `remove` to terminate the subscription before unmounting
    */
-  subscribe(lifespan, callback, context) {
+    subscribe(lifespan: { addUnmountCallback: Function }, callback: Function, context: Object) {
     invariant(
       typeof lifespan.addUnmountCallback === 'function',
       'Must provide a valid lifespan, which provides a way to add a ' +
@@ -169,7 +175,7 @@ class Subscribable {
    * Callback for the initial data resolution. Currently behaves the same as
    * `_handleEmit`, but we may eventually want to keep track of the difference
    */
-  _handleInitData(dataInput) {
+  _handleInitData(dataInput: Data) {
     var emitData = this._eventMapping(dataInput);
     this._lastData = emitData;
     this._internalEmitter.emit(SUBSCRIBABLE_INTERNAL_EVENT, emitData);
@@ -179,7 +185,7 @@ class Subscribable {
    * Handle new data emissions. Pass the data through our eventMapping
    * transformation, store it for later `get()`ing, and emit it for subscribers
    */
-  _handleEmit(dataInput) {
+  _handleEmit(dataInput: Data) {
     var emitData = this._eventMapping(dataInput);
     this._lastData = emitData;
     this._internalEmitter.emit(SUBSCRIBABLE_INTERNAL_EVENT, emitData);
@@ -280,12 +286,13 @@ Subscribable.Mixin = {
     if (!this._localSubscribables) {
       return;
     }
-    var emitterSubscribables;
     Object.keys(this._localSubscribables).forEach((eventEmitter) => {
-      emitterSubscribables = this._localSubscribables[eventEmitter];
-      Object.keys(emitterSubscribables).forEach((eventName) => {
-        emitterSubscribables[eventName].cleanup();
-      });
+      var emitterSubscribables = this._localSubscribables[eventEmitter];
+      if (emitterSubscribables) {
+        Object.keys(emitterSubscribables).forEach((eventName) => {
+          emitterSubscribables[eventName].cleanup();
+        });
+      }
     });
     this._localSubscribables = null;
   },
diff --git a/Libraries/Components/SwitchIOS/SwitchIOS.ios.js b/Libraries/Components/SwitchIOS/SwitchIOS.ios.js
index 417b29d11f..7022279475 100644
--- a/Libraries/Components/SwitchIOS/SwitchIOS.ios.js
+++ b/Libraries/Components/SwitchIOS/SwitchIOS.ios.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule SwitchIOS
+ * @flow
  *
  * This is a controlled component version of RCTSwitch.
  */
@@ -23,6 +24,13 @@ var merge = require('merge');
 
 var SWITCH = 'switch';
 
+type DefaultProps = {
+  value: boolean;
+  disabled: boolean;
+};
+
+type Event = Object;
+
 /**
  * Use `SwitchIOS` to render a boolean input on iOS.  This is
  * a controlled component, so you must hook in to the `onValueChange` callback
@@ -67,14 +75,14 @@ var SwitchIOS = React.createClass({
     tintColor: PropTypes.string,
   },
 
-  getDefaultProps: function() {
+  getDefaultProps: function(): DefaultProps {
     return {
       value: false,
       disabled: false,
     };
   },
 
-  _onChange: function(event) {
+  _onChange: function(event: Event) {
     this.props.onChange && this.props.onChange(event);
     this.props.onValueChange && this.props.onValueChange(event.nativeEvent.value);
 
diff --git a/Libraries/Components/TabBarIOS/TabBarIOS.ios.js b/Libraries/Components/TabBarIOS/TabBarIOS.ios.js
index 3e09a6c9b7..fa82dd4cbc 100644
--- a/Libraries/Components/TabBarIOS/TabBarIOS.ios.js
+++ b/Libraries/Components/TabBarIOS/TabBarIOS.ios.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule TabBarIOS
+ * @flow
  */
 'use strict';
 
diff --git a/Libraries/Components/TabBarIOS/TabBarItemIOS.ios.js b/Libraries/Components/TabBarIOS/TabBarItemIOS.ios.js
index 744c0a1f7d..11b02ab396 100644
--- a/Libraries/Components/TabBarIOS/TabBarItemIOS.ios.js
+++ b/Libraries/Components/TabBarIOS/TabBarItemIOS.ios.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule TabBarItemIOS
+ * @flow
  */
 'use strict';
 
@@ -43,7 +44,7 @@ var TabBarItemIOS = React.createClass({
     }
   },
 
-  componentWillReceiveProps: function(nextProps) {
+  componentWillReceiveProps: function(nextProps: { selected: boolean }) {
     if (this.state.hasBeenSelected || nextProps.selected) {
       this.setState({hasBeenSelected: true});
     }
diff --git a/Libraries/Components/TextInput/TextInput.ios.js b/Libraries/Components/TextInput/TextInput.ios.js
index 6affc40422..2653421be3 100644
--- a/Libraries/Components/TextInput/TextInput.ios.js
+++ b/Libraries/Components/TextInput/TextInput.ios.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule TextInput
+ * @flow
  */
 'use strict';
 
@@ -63,6 +64,12 @@ var notMultiline = {
   onSubmitEditing: true,
 };
 
+type DefaultProps = {
+  bufferDelay: number;
+};
+
+type Event = Object;
+
 /**
  * A foundational component for inputting text into the app via a
  * keyboard.  Props provide configurability for several features, such as auto-
@@ -206,12 +213,12 @@ var TextInput = React.createClass({
     validAttributes: RCTTextFieldAttributes,
   },
 
-  isFocused: function() {
+  isFocused: function(): boolean {
     return TextInputState.currentlyFocusedField() ===
       this.refs.input.getNativeNode();
   },
 
-  getDefaultProps: function() {
+  getDefaultProps: function(): DefaultProps {
     return {
       bufferDelay: 100,
     };
@@ -229,6 +236,8 @@ var TextInput = React.createClass({
     focusEmitter: React.PropTypes.instanceOf(EventEmitter),
   },
 
+  _focusSubscription: (undefined: ?Function),
+
   componentDidMount: function() {
     if (!this.context.focusEmitter) {
       if (this.props.autoFocus) {
@@ -255,7 +264,9 @@ var TextInput = React.createClass({
     this._focusSubscription && this._focusSubscription.remove();
   },
 
-  componentWillReceiveProps: function(newProps) {
+  _bufferTimeout: (undefined: ?number),
+
+  componentWillReceiveProps: function(newProps: {value: any}) {
     if (newProps.value !== this.props.value) {
       if (!this.isFocused()) {
         // Set the value immediately if the input is not focused since that
@@ -385,17 +396,17 @@ var TextInput = React.createClass({
     );
   },
 
-  _onFocus: function(event) {
+  _onFocus: function(event: Event) {
     if (this.props.onFocus) {
       this.props.onFocus(event);
     }
   },
 
-  _onPress: function(event) {
+  _onPress: function(event: Event) {
     this.focus();
   },
 
-  _onChange: function(event) {
+  _onChange: function(event: Event) {
     if (this.props.controlled && event.nativeEvent.text !== this.props.value) {
       this.refs.input.setNativeProps({text: this.props.value});
     }
@@ -403,14 +414,14 @@ var TextInput = React.createClass({
     this.props.onChangeText && this.props.onChangeText(event.nativeEvent.text);
   },
 
-  _onBlur: function(event) {
+  _onBlur: function(event: Event) {
     this.blur();
     if (this.props.onBlur) {
       this.props.onBlur(event);
     }
   },
 
-  _onSelectionChange: function(event) {
+  _onSelectionChange: function(event: Event) {
     if (this.props.selectionState) {
       var selection = event.nativeEvent.selection;
       this.props.selectionState.update(selection.start, selection.end);
@@ -418,7 +429,7 @@ var TextInput = React.createClass({
     this.props.onSelectionChange && this.props.onSelectionChange(event);
   },
 
-  _onTextInput: function(event) {
+  _onTextInput: function(event: Event) {
     this.props.onTextInput && this.props.onTextInput(event);
     var counter = event.nativeEvent.eventCounter;
     if (counter > this.state.mostRecentEventCounter) {
diff --git a/Libraries/Components/TextInput/TextInputState.js b/Libraries/Components/TextInput/TextInputState.js
index 5cd66c1f0c..7c5af440e7 100644
--- a/Libraries/Components/TextInput/TextInputState.js
+++ b/Libraries/Components/TextInput/TextInputState.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule TextInputState
+ * @flow
  *
  * This class is responsible for coordinating the "focused"
  * state for TextInputs. All calls relating to the keyboard
@@ -20,13 +21,13 @@ var TextInputState = {
    /**
    * Internal state
    */
-  _currentlyFocusedID: null,
+  _currentlyFocusedID: (null: ?string),
 
   /**
    * Returns the ID of the currently focused text field, if one exists
    * If no text field is focused it returns null
    */
-  currentlyFocusedField: function() {
+  currentlyFocusedField: function(): ?string {
     return this._currentlyFocusedID;
   },
 
@@ -35,7 +36,7 @@ var TextInputState = {
    * Focuses the specified text field
    * noop if the text field was already focused
    */
-  focusTextInput: function(textFieldID) {
+  focusTextInput: function(textFieldID: string) {
     if (this._currentlyFocusedID != textFieldID && textFieldID != null) {
       this._currentlyFocusedID = textFieldID;
       RCTUIManager.focus(textFieldID);
@@ -47,7 +48,7 @@ var TextInputState = {
    * Unfocuses the specified text field
    * noop if it wasn't focused
    */
-  blurTextInput: function(textFieldID) {
+  blurTextInput: function(textFieldID: string) {
     if (this._currentlyFocusedID == textFieldID && textFieldID != null) {
       this._currentlyFocusedID = null;
       RCTUIManager.blur(textFieldID);
diff --git a/Libraries/Components/Touchable/TouchableBounce.js b/Libraries/Components/Touchable/TouchableBounce.js
index c7e6af5d1d..d575657e9e 100644
--- a/Libraries/Components/Touchable/TouchableBounce.js
+++ b/Libraries/Components/Touchable/TouchableBounce.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule TouchableBounce
+ * @flow
  */
 'use strict';
 
@@ -20,6 +21,10 @@ var merge = require('merge');
 var copyProperties = require('copyProperties');
 var onlyChild = require('onlyChild');
 
+type State = {
+    animationID: ?number;
+};
+
 /**
  * When the scroll view is disabled, this defines how far your touch may move
  * off of the button, before deactivating the button. Once deactivated, try
@@ -47,11 +52,17 @@ var TouchableBounce = React.createClass({
     onPressAnimationComplete: React.PropTypes.func,
   },
 
-  getInitialState: function() {
+  getInitialState: function(): State {
     return merge(this.touchableGetInitialState(), {animationID: null});
   },
 
-  bounceTo: function(value, velocity, bounciness, fromValue, callback) {
+  bounceTo: function(
+    value: number,
+    velocity: number,
+    bounciness: number,
+    fromValue?: ?Function | number,
+    callback?: ?Function
+  ) {
     if (POPAnimation) {
       this.state.animationID && this.removeAnimation(this.state.animationID);
       var anim = {
@@ -60,6 +71,7 @@ var TouchableBounce = React.createClass({
         toValue: [value, value],
         velocity: [velocity, velocity],
         springBounciness: bounciness,
+        fromValue: (undefined: ?any),
       };
       if (fromValue) {
         anim.fromValue = [fromValue, fromValue];
@@ -90,8 +102,9 @@ var TouchableBounce = React.createClass({
   },
 
   touchableHandlePress: function() {
-    if (this.props.onPressWithCompletion) {
-      this.props.onPressWithCompletion(
+    var onPressWithCompletion = this.props.onPressWithCompletion;
+    if (onPressWithCompletion) {
+      onPressWithCompletion(
         this.bounceTo.bind(this, 1, 10, 10, 0.93, this.props.onPressAnimationComplete)
       );
       return;
@@ -101,11 +114,11 @@ var TouchableBounce = React.createClass({
     this.props.onPress && this.props.onPress();
   },
 
-  touchableGetPressRectOffset: function() {
+  touchableGetPressRectOffset: function(): typeof PRESS_RECT_OFFSET {
     return PRESS_RECT_OFFSET;   // Always make sure to predeclare a constant!
   },
 
-  touchableGetHighlightDelayMS: function() {
+  touchableGetHighlightDelayMS: function(): number {
     return 0;
   },
 
diff --git a/Libraries/Components/Touchable/TouchableHighlight.js b/Libraries/Components/Touchable/TouchableHighlight.js
index 6feaef0997..d2089fb563 100644
--- a/Libraries/Components/Touchable/TouchableHighlight.js
+++ b/Libraries/Components/Touchable/TouchableHighlight.js
@@ -10,6 +10,8 @@
  */
 'use strict';
 
+// Note (avik): add @flow when Flow supports spread properties in propTypes
+
 var NativeMethodsMixin = require('NativeMethodsMixin');
 var React = require('React');
 var ReactIOSViewAttributes = require('ReactIOSViewAttributes');
diff --git a/Libraries/Components/Touchable/TouchableOpacity.js b/Libraries/Components/Touchable/TouchableOpacity.js
index 065f1861a9..fd9d059714 100644
--- a/Libraries/Components/Touchable/TouchableOpacity.js
+++ b/Libraries/Components/Touchable/TouchableOpacity.js
@@ -10,6 +10,8 @@
  */
 'use strict';
 
+// Note (avik): add @flow when Flow supports spread properties in propTypes
+
 var NativeMethodsMixin = require('NativeMethodsMixin');
 var POPAnimationMixin = require('POPAnimationMixin');
 var React = require('React');
diff --git a/Libraries/Components/Touchable/TouchableWithoutFeedback.js b/Libraries/Components/Touchable/TouchableWithoutFeedback.js
index 53ac49d05e..1b1178ebbe 100644
--- a/Libraries/Components/Touchable/TouchableWithoutFeedback.js
+++ b/Libraries/Components/Touchable/TouchableWithoutFeedback.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule TouchableWithoutFeedback
+ * @flow
  */
 'use strict';
 
@@ -23,6 +24,7 @@ var onlyChild = require('onlyChild');
  */
 var PRESS_RECT_OFFSET = {top: 20, left: 20, right: 20, bottom: 30};
 
+type Event = Object;
 
 /**
  * Do not use unless you have a very good reason. All the elements that
@@ -51,7 +53,7 @@ var TouchableWithoutFeedback = React.createClass({
    * `Touchable.Mixin` self callbacks. The mixin will invoke these if they are
    * defined on your component.
    */
-  touchableHandlePress: function(e) {
+  touchableHandlePress: function(e: Event) {
     this.props.onPress && this.props.onPress(e);
   },
 
@@ -67,18 +69,19 @@ var TouchableWithoutFeedback = React.createClass({
     this.props.onLongPress && this.props.onLongPress();
   },
 
-  touchableGetPressRectOffset: function() {
+  touchableGetPressRectOffset: function(): typeof PRESS_RECT_OFFSET {
     return PRESS_RECT_OFFSET;   // Always make sure to predeclare a constant!
   },
 
-  touchableGetHighlightDelayMS: function() {
+  touchableGetHighlightDelayMS: function(): number {
     return 0;
   },
 
-  render: function() {
+  render: function(): ReactElement {
     // Note(vjeux): use cloneWithProps once React has been upgraded
     var child = onlyChild(this.props.children);
-    return React.cloneElement(child, {
+    // Note(avik): remove dynamic typecast once Flow has been upgraded
+    return (React: any).cloneElement(child, {
       accessible: true,
       testID: this.props.testID,
       onStartShouldSetResponder: this.touchableHandleStartShouldSetResponder,
diff --git a/Libraries/Components/Touchable/ensureComponentIsNative.js b/Libraries/Components/Touchable/ensureComponentIsNative.js
index 5a15f424f5..944093f78e 100644
--- a/Libraries/Components/Touchable/ensureComponentIsNative.js
+++ b/Libraries/Components/Touchable/ensureComponentIsNative.js
@@ -7,12 +7,13 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ensureComponentIsNative
+ * @flow
  */
 'use strict';
 
 var invariant = require('invariant');
 
-var ensureComponentIsNative = function(component) {
+var ensureComponentIsNative = function(component: any) {
   invariant(
     component && typeof component.setNativeProps === 'function',
     'Touchable child must either be native or forward setNativeProps to a ' +
diff --git a/Libraries/Components/View/View.js b/Libraries/Components/View/View.js
index 67a4ac9414..882adf4208 100644
--- a/Libraries/Components/View/View.js
+++ b/Libraries/Components/View/View.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule View
+ * @flow
  */
 'use strict';
 
diff --git a/Libraries/Components/View/ViewStylePropTypes.js b/Libraries/Components/View/ViewStylePropTypes.js
index e936f035a1..bb22c6b265 100644
--- a/Libraries/Components/View/ViewStylePropTypes.js
+++ b/Libraries/Components/View/ViewStylePropTypes.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ViewStylePropTypes
+ * @flow
  */
 'use strict';
 
diff --git a/Libraries/Components/WebView/WebView.ios.js b/Libraries/Components/WebView/WebView.ios.js
index 8768ab4041..867143b8c5 100644
--- a/Libraries/Components/WebView/WebView.ios.js
+++ b/Libraries/Components/WebView/WebView.ios.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule WebView
+ * @flow
  */
 'use strict';
 
@@ -24,6 +25,8 @@ var merge = require('merge');
 var PropTypes = React.PropTypes;
 var RCTWebViewManager = require('NativeModules').WebViewManager;
 
+var invariant = require('invariant');
+
 var RCT_WEBVIEW_REF = 'webview';
 
 var WebViewState = keyMirror({
@@ -41,6 +44,14 @@ var NavigationType = {
   other: RCTWebViewManager.NavigationType.Other,
 };
 
+type ErrorEvent = {
+  domain: any;
+  code: any;
+  description: any;
+}
+
+type Event = Object;
+
 var WebView = React.createClass({
   statics: {
     NavigationType: NavigationType,
@@ -61,7 +72,7 @@ var WebView = React.createClass({
   getInitialState: function() {
     return {
       viewState: WebViewState.IDLE,
-      lastErrorEvent: null,
+      lastErrorEvent: (null: ?ErrorEvent),
       startInLoadingState: true,
     };
   },
@@ -79,6 +90,10 @@ var WebView = React.createClass({
       otherView = this.props.renderLoading();
     } else if (this.state.viewState === WebViewState.ERROR) {
       var errorEvent = this.state.lastErrorEvent;
+      invariant(
+        errorEvent != null,
+        'lastErrorEvent expected to be non-null'
+      );
       otherView = this.props.renderError(
         errorEvent.domain,
         errorEvent.code,
@@ -132,21 +147,21 @@ var WebView = React.createClass({
    * We return an event with a bunch of fields including:
    *  url, title, loading, canGoBack, canGoForward
    */
-  updateNavigationState: function(event) {
+  updateNavigationState: function(event: Event) {
     if (this.props.onNavigationStateChange) {
       this.props.onNavigationStateChange(event.nativeEvent);
     }
   },
 
-  getWebWiewHandle: function() {
+  getWebWiewHandle: function(): any {
     return this.refs[RCT_WEBVIEW_REF].getNodeHandle();
   },
 
-  onLoadingStart: function(event) {
+  onLoadingStart: function(event: Event) {
     this.updateNavigationState(event);
   },
 
-  onLoadingError: function(event) {
+  onLoadingError: function(event: Event) {
     event.persist(); // persist this event because we need to store it
     console.error("encountered an error loading page", event.nativeEvent);
 
@@ -156,7 +171,7 @@ var WebView = React.createClass({
     });
   },
 
-  onLoadingFinish: function(event) {
+  onLoadingFinish: function(event: Event) {
     this.setState({
       viewState: WebViewState.IDLE,
     });