diff --git a/.flowconfig b/.flowconfig
index 28625456dcd07a..c4265b9b2c6f0c 100644
--- a/.flowconfig
+++ b/.flowconfig
@@ -10,7 +10,8 @@
 # Ignore react-tools where there are overlaps, but don't ignore anything that
 # react-native relies on
 .*/node_modules/react-tools/src/vendor/core/ExecutionEnvironment.js
-.*/node_modules/react-tools/src/browser/.*
+.*/node_modules/react-tools/src/browser/eventPlugins/ResponderEventPlugin.js
+.*/node_modules/react-tools/src/browser/ui/React.js
 .*/node_modules/react-tools/src/core/ReactInstanceHandles.js
 .*/node_modules/react-tools/src/event/EventPropagators.js
 
diff --git a/Libraries/ReactIOS/IOSDefaultEventPluginOrder.js b/Libraries/ReactIOS/IOSDefaultEventPluginOrder.js
index b2336692087594..80098fc414f308 100644
--- a/Libraries/ReactIOS/IOSDefaultEventPluginOrder.js
+++ b/Libraries/ReactIOS/IOSDefaultEventPluginOrder.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule IOSDefaultEventPluginOrder
+ * @flow
  */
 'use strict';
 
diff --git a/Libraries/ReactIOS/IOSNativeBridgeEventPlugin.js b/Libraries/ReactIOS/IOSNativeBridgeEventPlugin.js
index c41ae82ab18eb8..b585db5a76f810 100644
--- a/Libraries/ReactIOS/IOSNativeBridgeEventPlugin.js
+++ b/Libraries/ReactIOS/IOSNativeBridgeEventPlugin.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule IOSNativeBridgeEventPlugin
+ * @flow
  */
 
 "use strict";
@@ -51,10 +52,11 @@ var IOSNativeBridgeEventPlugin = {
    * @see {EventPluginHub.extractEvents}
    */
   extractEvents: function(
-      topLevelType,
-      topLevelTarget,
-      topLevelTargetID,
-      nativeEvent) {
+    topLevelType: string,
+    topLevelTarget: EventTarget,
+    topLevelTargetID: string,
+    nativeEvent: Event
+  ): ?Object {
     var bubbleDispatchConfig = customBubblingEventTypes[topLevelType];
     var directDispatchConfig = customDirectEventTypes[topLevelType];
     var event = SyntheticEvent.getPooled(
diff --git a/Libraries/ReactIOS/NativeMethodsMixin.js b/Libraries/ReactIOS/NativeMethodsMixin.js
index 3dbe233ee9e18d..ec72a0b4f4696b 100644
--- a/Libraries/ReactIOS/NativeMethodsMixin.js
+++ b/Libraries/ReactIOS/NativeMethodsMixin.js
@@ -7,10 +7,10 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule NativeMethodsMixin
+ * @flow
  */
 'use strict';
 
-var NativeModules = require('NativeModules');
 var NativeModules = require('NativeModules');
 var RCTPOPAnimationManager = NativeModules.POPAnimationManager;
 var RCTUIManager = NativeModules.UIManager;
@@ -20,7 +20,26 @@ var flattenStyle = require('flattenStyle');
 var invariant = require('invariant');
 var mergeFast = require('mergeFast');
 
-var animationIDInvariant = function(funcName, anim) {
+type MeasureOnSuccessCallback = (
+  x: number,
+  y: number,
+  width: number,
+  height: number,
+  pageX: number,
+  pageY: number
+) => void
+
+type MeasureLayoutOnSuccessCallback = (
+  left: number,
+  top: number,
+  width: number,
+  height: number
+) => void
+
+var animationIDInvariant = function(
+  funcName: string,
+  anim: number
+) {
   invariant(
     anim,
     funcName + ' must be called with a valid animation ID returned from' +
@@ -29,21 +48,25 @@ var animationIDInvariant = function(funcName, anim) {
 };
 
 var NativeMethodsMixin = {
-  addAnimation: function(anim, callback) {
+  addAnimation: function(anim: number, callback?: (finished: bool) => void) {
     animationIDInvariant('addAnimation', anim);
     RCTPOPAnimationManager.addAnimation(this.getNodeHandle(), anim, callback);
   },
 
-  removeAnimation: function(anim) {
+  removeAnimation: function(anim: number) {
     animationIDInvariant('removeAnimation', anim);
     RCTPOPAnimationManager.removeAnimation(this.getNodeHandle(), anim);
   },
 
-  measure: function(callback) {
+  measure: function(callback: MeasureOnSuccessCallback) {
     RCTUIManager.measure(this.getNodeHandle(), callback);
   },
 
-  measureLayout: function(relativeToNativeNode, onSuccess, onFail) {
+  measureLayout: function(
+    relativeToNativeNode: number,
+    onSuccess: MeasureLayoutOnSuccessCallback,
+    onFail: () => void /* currently unused */
+  ) {
     RCTUIManager.measureLayout(
       this.getNodeHandle(),
       relativeToNativeNode,
@@ -57,7 +80,7 @@ var NativeMethodsMixin = {
    * in future diff process, this means that if you do not include them in the
    * next render, they will remain active.
    */
-  setNativeProps: function(nativeProps) {
+  setNativeProps: function(nativeProps: Object) {
     // nativeProps contains a style attribute that's going to be flattened
     // and all the attributes expanded in place. In order to make this
     // process do as few allocations and copies as possible, we return
@@ -111,15 +134,19 @@ function throwOnStylesProp(component, props) {
   }
 }
 if (__DEV__) {
+  // hide this from Flow since we can't define these properties outside of
+  // __DEV__ without actually implementing them (setting them to undefined
+  // isn't allowed by ReactClass)
+  var NativeMethodsMixin_DEV = (NativeMethodsMixin: any);
   invariant(
-    !NativeMethodsMixin.componentWillMount &&
-    !NativeMethodsMixin.componentWillReceiveProps,
+    !NativeMethodsMixin_DEV.componentWillMount &&
+    !NativeMethodsMixin_DEV.componentWillReceiveProps,
     'Do not override existing functions.'
   );
-  NativeMethodsMixin.componentWillMount = function () {
+  NativeMethodsMixin_DEV.componentWillMount = function () {
     throwOnStylesProp(this, this.props);
   };
-  NativeMethodsMixin.componentWillReceiveProps = function (newProps) {
+  NativeMethodsMixin_DEV.componentWillReceiveProps = function (newProps) {
     throwOnStylesProp(this, newProps);
   };
 }
diff --git a/Libraries/ReactIOS/React.js b/Libraries/ReactIOS/React.js
index 34f19013866289..ce9de085221fdd 100644
--- a/Libraries/ReactIOS/React.js
+++ b/Libraries/ReactIOS/React.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule React
+ * @flow
  */
 
 "use strict";
diff --git a/Libraries/ReactIOS/ReactIOS.js b/Libraries/ReactIOS/ReactIOS.js
index e1c9480650a83f..02857742933892 100644
--- a/Libraries/ReactIOS/ReactIOS.js
+++ b/Libraries/ReactIOS/ReactIOS.js
@@ -7,8 +7,8 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ReactIOS
+ * @flow
  */
-
 "use strict";
 
 var ReactChildren = require('ReactChildren');
@@ -51,7 +51,7 @@ var resolveDefaultProps = function(element) {
 };
 
 // Experimental optimized element creation
-var augmentElement = function(element) {
+var augmentElement = function(element: ReactElement) {
   if (__DEV__) {
     invariant(
       false,
@@ -67,7 +67,7 @@ var augmentElement = function(element) {
   return element;
 };
 
-var render = function(component, mountInto) {
+var render = function(component: ReactComponent, mountInto: number) {
   ReactIOSMount.renderComponent(component, mountInto);
 };
 
diff --git a/Libraries/ReactIOS/ReactIOSComponentEnvironment.js b/Libraries/ReactIOS/ReactIOSComponentEnvironment.js
index 664ebb6ece9874..0dc0b1d1c929e6 100644
--- a/Libraries/ReactIOS/ReactIOSComponentEnvironment.js
+++ b/Libraries/ReactIOS/ReactIOSComponentEnvironment.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ReactIOSComponentEnvironment
+ * @flow
  */
 'use strict';
 
diff --git a/Libraries/ReactIOS/ReactIOSComponentMixin.js b/Libraries/ReactIOS/ReactIOSComponentMixin.js
index d8044e5eb67eed..94c708a433e863 100644
--- a/Libraries/ReactIOS/ReactIOSComponentMixin.js
+++ b/Libraries/ReactIOS/ReactIOSComponentMixin.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ReactIOSComponentMixin
+ * @flow
  */
 'use strict';
 
diff --git a/Libraries/ReactIOS/ReactIOSDOMIDOperations.js b/Libraries/ReactIOS/ReactIOSDOMIDOperations.js
index 7e266530aed23d..7d421442f5325b 100644
--- a/Libraries/ReactIOS/ReactIOSDOMIDOperations.js
+++ b/Libraries/ReactIOS/ReactIOSDOMIDOperations.js
@@ -7,7 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ReactIOSDOMIDOperations
- * @typechecks static-only
+ * @flow
  */
 
 "use strict";
diff --git a/Libraries/ReactIOS/ReactIOSDefaultInjection.js b/Libraries/ReactIOS/ReactIOSDefaultInjection.js
index dd67987cccb514..d6b81da2cdcef3 100644
--- a/Libraries/ReactIOS/ReactIOSDefaultInjection.js
+++ b/Libraries/ReactIOS/ReactIOSDefaultInjection.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ReactIOSDefaultInjection
+ * @flow
  */
 
 "use strict";
diff --git a/Libraries/ReactIOS/createReactIOSNativeComponentClass.js b/Libraries/ReactIOS/createReactIOSNativeComponentClass.js
index 19217cb72078fe..5a5af04dc815da 100644
--- a/Libraries/ReactIOS/createReactIOSNativeComponentClass.js
+++ b/Libraries/ReactIOS/createReactIOSNativeComponentClass.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule createReactIOSNativeComponentClass
+ * @flow
  */
 
 "use strict";
@@ -14,11 +15,19 @@
 var ReactElement = require('ReactElement');
 var ReactIOSNativeComponent = require('ReactIOSNativeComponent');
 
+// See also ReactIOSNativeComponent
+type ReactIOSNativeComponentViewConfig = {
+  validAttributes: Object;
+  uiViewClassName: string;
+}
+
 /**
  * @param {string} config iOS View configuration.
  * @private
  */
-var createReactIOSNativeComponentClass = function(viewConfig) {
+var createReactIOSNativeComponentClass = function(
+  viewConfig: ReactIOSNativeComponentViewConfig
+): Function { // returning Function is lossy :/
   var Constructor = function(element) {
     this._currentElement = element;
 
diff --git a/Libraries/ReactIOS/diffRawProperties.js b/Libraries/ReactIOS/diffRawProperties.js
index 2be542aaa76818..3a5de284f4910e 100644
--- a/Libraries/ReactIOS/diffRawProperties.js
+++ b/Libraries/ReactIOS/diffRawProperties.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule diffRawProperties
+ * @flow
  */
 'use strict';
 
@@ -21,34 +22,41 @@
  * previous. These properties are as supplied to component construction.
  * @return {?object}
  */
-function diffRawProperties(updatePayload, prevProps, nextProps, validAttributes) {
+function diffRawProperties(
+  updatePayload: ?Object,
+  prevProps: ?Object,
+  nextProps: ?Object,
+  validAttributes: Object
+): ?Object {
   var validAttributeConfig;
   var nextProp;
   var prevProp;
   var isScalar;
   var shouldUpdate;
 
-  for (var propKey in nextProps) {
-    validAttributeConfig = validAttributes[propKey];
-    if (!validAttributeConfig) {
-      continue; // not a valid native prop
-    }
-    prevProp = prevProps && prevProps[propKey];
-    nextProp = nextProps[propKey];
-    if (prevProp !== nextProp) {
-      // If you want a property's diff to be detected, you must configure it
-      // to be so - *or* it must be a scalar property. For now, we'll allow
-      // creation with any attribute that is not scalar, but we should
-      // eventually even reject those unless they are properly configured.
-      isScalar = typeof nextProp !== 'object' || nextProp === null;
-      shouldUpdate = isScalar ||
-        !prevProp ||
-        validAttributeConfig.diff &&
-        validAttributeConfig.diff(prevProp, nextProp);
+  if (nextProps) {
+    for (var propKey in nextProps) {
+      validAttributeConfig = validAttributes[propKey];
+      if (!validAttributeConfig) {
+        continue; // not a valid native prop
+      }
+      prevProp = prevProps && prevProps[propKey];
+      nextProp = nextProps[propKey];
+      if (prevProp !== nextProp) {
+        // If you want a property's diff to be detected, you must configure it
+        // to be so - *or* it must be a scalar property. For now, we'll allow
+        // creation with any attribute that is not scalar, but we should
+        // eventually even reject those unless they are properly configured.
+        isScalar = typeof nextProp !== 'object' || nextProp === null;
+        shouldUpdate = isScalar ||
+          !prevProp ||
+          validAttributeConfig.diff &&
+          validAttributeConfig.diff(prevProp, nextProp);
 
-      if (shouldUpdate) {
-        updatePayload = updatePayload || {};
-        updatePayload[propKey] = nextProp;
+        if (shouldUpdate) {
+          updatePayload = updatePayload || {};
+          updatePayload[propKey] = nextProp;
+        }
       }
     }
   }
@@ -56,31 +64,33 @@ function diffRawProperties(updatePayload, prevProps, nextProps, validAttributes)
   // Also iterate through all the previous props to catch any that have been
   // removed and make sure native gets the signal so it can reset them to the
   // default.
-  for (var propKey in prevProps) {
-    validAttributeConfig = validAttributes[propKey];
-    if (!validAttributeConfig) {
-      continue; // not a valid native prop
-    }
-    if (updatePayload && updatePayload[propKey] !== undefined) {
-      continue; // Prop already specified
-    }
-    prevProp = prevProps[propKey];
-    nextProp = nextProps && nextProps[propKey];
-    if (prevProp !== nextProp) {
-      if (nextProp === undefined) {
-        nextProp = null; // null is a sentinel we explicitly send to native
+  if (prevProps) {
+    for (var propKey in prevProps) {
+      validAttributeConfig = validAttributes[propKey];
+      if (!validAttributeConfig) {
+        continue; // not a valid native prop
+      }
+      if (updatePayload && updatePayload[propKey] !== undefined) {
+        continue; // Prop already specified
       }
-      // If you want a property's diff to be detected, you must configure it
-      // to be so - *or* it must be a scalar property. For now, we'll allow
-      // creation with any attribute that is not scalar, but we should
-      // eventually even reject those unless they are properly configured.
-      isScalar = typeof nextProp !== 'object' || nextProp === null;
-      shouldUpdate = isScalar && prevProp !== nextProp ||
-        validAttributeConfig.diff &&
-        validAttributeConfig.diff(prevProp, nextProp);
-      if (shouldUpdate) {
-        updatePayload = updatePayload || {};
-        updatePayload[propKey] = nextProp;
+      prevProp = prevProps[propKey];
+      nextProp = nextProps && nextProps[propKey];
+      if (prevProp !== nextProp) {
+        if (nextProp === undefined) {
+          nextProp = null; // null is a sentinel we explicitly send to native
+        }
+        // If you want a property's diff to be detected, you must configure it
+        // to be so - *or* it must be a scalar property. For now, we'll allow
+        // creation with any attribute that is not scalar, but we should
+        // eventually even reject those unless they are properly configured.
+        isScalar = typeof nextProp !== 'object' || nextProp === null;
+        shouldUpdate = isScalar && prevProp !== nextProp ||
+          validAttributeConfig.diff &&
+          validAttributeConfig.diff(prevProp, nextProp);
+        if (shouldUpdate) {
+          updatePayload = updatePayload || {};
+          updatePayload[propKey] = nextProp;
+        }
       }
     }
   }
diff --git a/Libraries/react-native/react-native-interface.js b/Libraries/react-native/react-native-interface.js
index 2ace792922be62..6408526b812e6a 100644
--- a/Libraries/react-native/react-native-interface.js
+++ b/Libraries/react-native/react-native-interface.js
@@ -12,3 +12,7 @@
 // see also react-native.js
 
 declare var __DEV__: boolean;
+
+declare var __REACT_DEVTOOLS_GLOBAL_HOOK__: any; /*?{
+  inject: ?((stuff: Object) => void)
+};*/