diff --git a/Libraries/Animation/POPAnimationMixin.js b/Libraries/Animation/POPAnimationMixin.js
index a1ded9f95..213023290 100644
--- a/Libraries/Animation/POPAnimationMixin.js
+++ b/Libraries/Animation/POPAnimationMixin.js
@@ -11,14 +11,18 @@
  */
 'use strict';
 
-var POPAnimation = require('POPAnimation');
+var POPAnimationOrNull = require('POPAnimation');
 
-if (!POPAnimation) {
+if (!POPAnimationOrNull) {
   // POP animation isn't available in the OSS fork - this is a temporary
   // workaround to enable its availability to be determined at runtime.
   module.exports = (null : ?{});
 } else {
 
+// At this point, POPAnimationOrNull is guaranteed to be
+// non-null. Bring it local to preserve type refinement.
+var POPAnimation = POPAnimationOrNull;
+
 var invariant = require('invariant');
 var warning = require('warning');
 
diff --git a/Libraries/BatchedBridge/BatchedBridgedModules/POPAnimation.js b/Libraries/BatchedBridge/BatchedBridgedModules/POPAnimation.js
index 2bd2ebd03..959bf2383 100644
--- a/Libraries/BatchedBridge/BatchedBridgedModules/POPAnimation.js
+++ b/Libraries/BatchedBridge/BatchedBridgedModules/POPAnimation.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule POPAnimation
+ * @flow
  */
 'use strict';
 
@@ -14,7 +15,7 @@ var RCTPOPAnimationManager = require('NativeModules').POPAnimationManager;
 if (!RCTPOPAnimationManager) {
   // POP animation isn't available in the OSS fork - this is a temporary
   // workaround to enable its availability to be determined at runtime.
-  module.exports = null;
+  module.exports = (null: ?Object);
 } else {
 
 var ReactPropTypes = require('ReactPropTypes');
@@ -64,6 +65,20 @@ var Types = {
   spring: RCTTypes.spring,
 };
 
+type Attrs = {
+  type?: $Enum<typeof Types>;
+  property?: $Enum<typeof Properties>;
+  fromValue?: any;
+  toValue?: any;
+  duration?: any;
+  velocity?: any;
+  deceleration?: any;
+  springBounciness?: any;
+  dynamicsFriction?: any;
+  dynamicsMass?: any;
+  dynamicsTension?: any;
+}
+
 var POPAnimation = {
   Types: Types,
   Properties: Properties,
@@ -83,11 +98,11 @@ var POPAnimation = {
   }),
 
   lastUsedTag: 0,
-  allocateTagForAnimation: function() {
+  allocateTagForAnimation: function(): number {
     return ++this.lastUsedTag;
   },
 
-  createAnimation: function(typeName, attrs) {
+  createAnimation: function(typeName: number, attrs: Attrs): number {
     var tag = this.allocateTagForAnimation();
 
     if (__DEV__) {
@@ -107,35 +122,35 @@ var POPAnimation = {
     return tag;
   },
 
-  createSpringAnimation: function(attrs) {
+  createSpringAnimation: function(attrs: Attrs): number {
     return this.createAnimation(this.Types.spring, attrs);
   },
 
-  createDecayAnimation: function(attrs) {
+  createDecayAnimation: function(attrs: Attrs): number {
     return this.createAnimation(this.Types.decay, attrs);
   },
 
-  createLinearAnimation: function(attrs) {
+  createLinearAnimation: function(attrs: Attrs): number {
     return this.createAnimation(this.Types.linear, attrs);
   },
 
-  createEaseInAnimation: function(attrs) {
+  createEaseInAnimation: function(attrs: Attrs): number {
     return this.createAnimation(this.Types.easeIn, attrs);
   },
 
-  createEaseOutAnimation: function(attrs) {
+  createEaseOutAnimation: function(attrs: Attrs): number {
     return this.createAnimation(this.Types.easeOut, attrs);
   },
 
-  createEaseInEaseOutAnimation: function(attrs) {
+  createEaseInEaseOutAnimation: function(attrs: Attrs): number {
     return this.createAnimation(this.Types.easeInEaseOut, attrs);
   },
 
-  addAnimation: function(nodeHandle, anim, callback) {
+  addAnimation: function(nodeHandle: any, anim: number, callback: Function) {
     RCTPOPAnimationManager.addAnimation(nodeHandle, anim, callback);
   },
 
-  removeAnimation: function(nodeHandle, anim) {
+  removeAnimation: function(nodeHandle: any, anim: number) {
     RCTPOPAnimationManager.removeAnimation(nodeHandle, anim);
   },
 };
diff --git a/Libraries/Geolocation/Geolocation.ios.js b/Libraries/Geolocation/Geolocation.ios.js
index eb33fbbbe..6a022f76f 100644
--- a/Libraries/Geolocation/Geolocation.ios.js
+++ b/Libraries/Geolocation/Geolocation.ios.js
@@ -37,7 +37,8 @@ var Geolocation = {
   getCurrentPosition: function(
     geo_success: Function,
     geo_error?: Function,
-    geo_options?: Object) {
+    geo_options?: Object
+  ) {
     invariant(
       typeof geo_success === 'function',
       'Must provide a valid geo_success callback.'
diff --git a/Libraries/Image/Image.ios.js b/Libraries/Image/Image.ios.js
index 1e2589723..ed857584d 100644
--- a/Libraries/Image/Image.ios.js
+++ b/Libraries/Image/Image.ios.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule Image
+ * @flow
  */
 'use strict';
 
@@ -106,7 +107,9 @@ var Image = React.createClass({
 
   render: function() {
     var style = flattenStyle([styles.base, this.props.style]);
+    invariant(style, "style must be initialized");
     var source = this.props.source;
+    invariant(source, "source must be initialized");
     var isNetwork = source.uri && source.uri.match(/^https?:/);
     invariant(
       !(isNetwork && source.isStatic),
diff --git a/Libraries/Image/ImageResizeMode.js b/Libraries/Image/ImageResizeMode.js
index 368f4dfb8..9a7a2f954 100644
--- a/Libraries/Image/ImageResizeMode.js
+++ b/Libraries/Image/ImageResizeMode.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ImageResizeMode
+ * @flow
  */
 'use strict';
 
diff --git a/Libraries/Image/ImageStylePropTypes.js b/Libraries/Image/ImageStylePropTypes.js
index b48ac8653..4e361d9de 100644
--- a/Libraries/Image/ImageStylePropTypes.js
+++ b/Libraries/Image/ImageStylePropTypes.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ImageStylePropTypes
+ * @flow
  */
 'use strict';
 
@@ -39,8 +40,8 @@ var unsupportedProps = Object.keys({
   paddingHorizontal: null,
 });
 
-for (var key in unsupportedProps) {
-  delete ImageStylePropTypes[key];
+for (var i = 0; i < unsupportedProps.length; i++) {
+  delete ImageStylePropTypes[unsupportedProps[i]];
 }
 
 module.exports = ImageStylePropTypes;
diff --git a/Libraries/Interaction/InteractionManager.js b/Libraries/Interaction/InteractionManager.js
index 3a104bad2..6aef690dd 100644
--- a/Libraries/Interaction/InteractionManager.js
+++ b/Libraries/Interaction/InteractionManager.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule InteractionManager
+ * @flow
  */
 'use strict';
 
@@ -70,7 +71,7 @@ var InteractionManager = {
   /**
    * Schedule a function to run after all interactions have completed.
    */
-  runAfterInteractions(callback) {
+  runAfterInteractions(callback: Function) {
     invariant(
       typeof callback === 'function',
       'Must specify a function to schedule.'
@@ -82,7 +83,7 @@ var InteractionManager = {
   /**
    * Notify manager that an interaction has started.
    */
-  createInteractionHandle() {
+  createInteractionHandle(): number {
     scheduleUpdate();
     var handle = ++_inc;
     _addInteractionSet.add(handle);
@@ -92,7 +93,7 @@ var InteractionManager = {
   /**
    * Notify manager that an interaction has completed.
    */
-  clearInteractionHandle(handle) {
+  clearInteractionHandle(handle: number) {
     invariant(
       !!handle,
       'Must provide a handle to clear.'
diff --git a/Libraries/Interaction/InteractionMixin.js b/Libraries/Interaction/InteractionMixin.js
index 633159c1f..b92120f90 100644
--- a/Libraries/Interaction/InteractionMixin.js
+++ b/Libraries/Interaction/InteractionMixin.js
@@ -2,6 +2,7 @@
  * Copyright 2004-present Facebook. All Rights Reserved.
  *
  * @providesModule InteractionMixin
+ * @flow
  */
 'use strict';
 
@@ -21,7 +22,7 @@ var InteractionMixin = {
     }
   },
 
-  _interactionMixinHandles: [],
+  _interactionMixinHandles: ([]: Array<number>),
 
   createInteractionHandle: function() {
     var handle = InteractionManager.createInteractionHandle();
@@ -29,7 +30,7 @@ var InteractionMixin = {
     return handle;
   },
 
-  clearInteractionHandle: function(clearHandle) {
+  clearInteractionHandle: function(clearHandle: number) {
     InteractionManager.clearInteractionHandle(clearHandle);
     this._interactionMixinHandles = this._interactionMixinHandles.filter(
       handle => handle !== clearHandle
@@ -41,7 +42,7 @@ var InteractionMixin = {
    *
    * @param {function} callback
    */
-  runAfterInteractions: function(callback) {
+  runAfterInteractions: function(callback: Function) {
     InteractionManager.runAfterInteractions(callback);
   },
 };
diff --git a/Libraries/JavaScriptAppEngine/Initialization/ExceptionsManager.js b/Libraries/JavaScriptAppEngine/Initialization/ExceptionsManager.js
index 9b2a43bcc..7dadeb5bb 100644
--- a/Libraries/JavaScriptAppEngine/Initialization/ExceptionsManager.js
+++ b/Libraries/JavaScriptAppEngine/Initialization/ExceptionsManager.js
@@ -7,6 +7,7 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ExceptionsManager
+ * @flow
  */
 'use strict';
 
@@ -18,7 +19,13 @@ var parseErrorStack = require('parseErrorStack');
 
 var sourceMapPromise;
 
-function handleException(e) {
+type Exception = {
+  sourceURL: string;
+  line: number;
+  message: string;
+}
+
+function handleException(e: Exception) {
   var stack = parseErrorStack(e);
   console.error(
     'Error: ' +