diff --git a/Examples/UIExplorer/NavigatorIOSExample.js b/Examples/UIExplorer/NavigatorIOSExample.js
index 7b92346054..9f6065cbe9 100644
--- a/Examples/UIExplorer/NavigatorIOSExample.js
+++ b/Examples/UIExplorer/NavigatorIOSExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
@@ -150,7 +151,7 @@ var NavigatorIOSExample = React.createClass({
     });
   },
 
-  _renderRow: function(title, onPress) {
+  _renderRow: function(title: string, onPress: Function) {
     return (
       <View>
         <TouchableHighlight onPress={onPress}>
diff --git a/Examples/UIExplorer/NetInfoExample.js b/Examples/UIExplorer/NetInfoExample.js
index 017da9921e..dabff174e9 100644
--- a/Examples/UIExplorer/NetInfoExample.js
+++ b/Examples/UIExplorer/NetInfoExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
@@ -120,16 +121,16 @@ exports.examples = [
   {
     title: 'NetInfo.isConnected',
     description: 'Asyncronously load and observe connectivity',
-    render() { return <IsConnected />; }
+    render(): ReactElement { return <IsConnected />; }
   },
   {
     title: 'NetInfo.reachabilityIOS',
     description: 'Asyncronously load and observe iOS reachability',
-    render() { return <ReachabilityCurrent />; }
+    render(): ReactElement { return <ReachabilityCurrent />; }
   },
   {
     title: 'NetInfo.reachabilityIOS',
     description: 'Observed updates to iOS reachability',
-    render() { return <ReachabilitySubscription />; }
+    render(): ReactElement { return <ReachabilitySubscription />; }
   },
 ];
diff --git a/Examples/UIExplorer/PickerExample.js b/Examples/UIExplorer/PickerExample.js
index 53f717bf36..bbe1ca4fc6 100644
--- a/Examples/UIExplorer/PickerExample.js
+++ b/Examples/UIExplorer/PickerExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
@@ -105,7 +106,7 @@ exports.description = 'Render lists of selectable options with UIPickerView.';
 exports.examples = [
 {
   title: '<PickerIOS>',
-  render: function() {
+  render: function(): ReactElement {
     return <PickerExample />;
   },
 }];
diff --git a/Examples/UIExplorer/PointerEventsExample.js b/Examples/UIExplorer/PointerEventsExample.js
index be9f5a5215..e83d88d1de 100644
--- a/Examples/UIExplorer/PointerEventsExample.js
+++ b/Examples/UIExplorer/PointerEventsExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
diff --git a/Examples/UIExplorer/ScrollViewExample.js b/Examples/UIExplorer/ScrollViewExample.js
index 0dca6b3be6..2e8045afb7 100644
--- a/Examples/UIExplorer/ScrollViewExample.js
+++ b/Examples/UIExplorer/ScrollViewExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
diff --git a/Examples/UIExplorer/SliderIOSExample.js b/Examples/UIExplorer/SliderIOSExample.js
index bc58ccec71..b7db6bcdd8 100644
--- a/Examples/UIExplorer/SliderIOSExample.js
+++ b/Examples/UIExplorer/SliderIOSExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
@@ -50,6 +51,6 @@ exports.description = 'Slider input for numeric values';
 exports.examples = [
   {
     title: 'SliderIOS',
-    render() { return <SliderExample />; }
+    render(): ReactElement { return <SliderExample />; }
   }
 ];
diff --git a/Examples/UIExplorer/StatusBarIOSExample.js b/Examples/UIExplorer/StatusBarIOSExample.js
index bca275501a..638883b995 100644
--- a/Examples/UIExplorer/StatusBarIOSExample.js
+++ b/Examples/UIExplorer/StatusBarIOSExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
diff --git a/Examples/UIExplorer/SwitchExample.js b/Examples/UIExplorer/SwitchExample.js
index 23538e1698..2cee746628 100644
--- a/Examples/UIExplorer/SwitchExample.js
+++ b/Examples/UIExplorer/SwitchExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
@@ -118,22 +119,22 @@ exports.description = 'Native boolean input';
 exports.examples = [
   {
     title: 'Switches can be set to true or false',
-    render() { return <BasicSwitchExample />; }
+    render(): ReactElement { return <BasicSwitchExample />; }
   },
   {
     title: 'Switches can be disabled',
-    render() { return <DisabledSwitchExample />; }
+    render(): ReactElement { return <DisabledSwitchExample />; }
   },
   {
     title: 'Custom colors can be provided',
-    render() { return <ColorSwitchExample />; }
+    render(): ReactElement { return <ColorSwitchExample />; }
   },
   {
     title: 'Change events can be detected',
-    render() { return <EventSwitchExample />; }
+    render(): ReactElement { return <EventSwitchExample />; }
   },
   {
     title: 'Switches are controlled components',
-    render() { return <SwitchIOS />; }
+    render(): ReactElement { return <SwitchIOS />; }
   }
 ];
diff --git a/Examples/UIExplorer/TextExample.ios.js b/Examples/UIExplorer/TextExample.ios.js
index 1894b31ff1..9c9826772d 100644
--- a/Examples/UIExplorer/TextExample.ios.js
+++ b/Examples/UIExplorer/TextExample.ios.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
@@ -199,7 +200,7 @@ exports.examples = [
   },
 }, {
   title: 'Toggling Attributes',
-  render: function() {
+  render: function(): ReactElement {
     return <AttributeToggler />;
   },
 }, {
diff --git a/Examples/UIExplorer/TextInputExample.js b/Examples/UIExplorer/TextInputExample.js
index bce5de9d8c..fec6f84511 100644
--- a/Examples/UIExplorer/TextInputExample.js
+++ b/Examples/UIExplorer/TextInputExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
@@ -164,7 +165,7 @@ exports.examples = [
   },
   {
     title: 'Event handling',
-    render: () => <TextEventsExample />,
+    render: function(): ReactElement { return <TextEventsExample /> },
   },
   {
     title: 'Colored input text',
diff --git a/Examples/UIExplorer/TimerExample.js b/Examples/UIExplorer/TimerExample.js
index 6d48738d4d..7cd576e6c4 100644
--- a/Examples/UIExplorer/TimerExample.js
+++ b/Examples/UIExplorer/TimerExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
@@ -31,6 +32,12 @@ var Button = React.createClass({
 var TimerTester = React.createClass({
   mixins: [TimerMixin],
 
+  _ii: 0,
+  _iters: 0,
+  _start: 0,
+  _timerFn: (null : ?(() => any)),
+  _handle: (null : any),
+
   render: function() {
     var args = 'fn' + (this.props.dt !== undefined ? ', ' + this.props.dt : '');
     return (
@@ -71,7 +78,7 @@ var TimerTester = React.createClass({
         'Elapsed time: ' + e + ' ms\n' + (e / this._ii) + ' ms / iter';
       console.log(msg);
       AlertIOS.alert(msg);
-      this._start = null;
+      this._start = 0;
       this.forceUpdate(() => { this._ii = 0; });
       return;
     }
@@ -153,7 +160,7 @@ exports.examples = [
     title: 'this.setInterval(fn, t)',
     description: 'Execute function fn every t milliseconds until cancelled ' +
       'or component is unmounted.',
-    render: function() {
+    render: function(): ReactElement {
       var IntervalExample = React.createClass({
         getInitialState: function() {
           return {
diff --git a/Examples/UIExplorer/TouchableExample.js b/Examples/UIExplorer/TouchableExample.js
index 4226ec18a9..01e8bbfb1b 100644
--- a/Examples/UIExplorer/TouchableExample.js
+++ b/Examples/UIExplorer/TouchableExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
@@ -53,14 +54,14 @@ exports.examples = [
   },
 }, {
   title: '<Text onPress={fn}> with highlight',
-  render: function() {
+  render: function(): ReactElement {
     return <TextOnPressBox />;
   },
 }, {
   title: 'Touchable feedback events',
   description: '<Touchable*> components accept onPress, onPressIn, ' +
     'onPressOut, and onLongPress as props.',
-  render: function() {
+  render: function(): ReactElement {
     return <TouchableFeedbackEvents />;
   },
 }];
diff --git a/Examples/UIExplorer/UIExplorerApp.js b/Examples/UIExplorer/UIExplorerApp.js
index c234d54b69..97da6d10f1 100644
--- a/Examples/UIExplorer/UIExplorerApp.js
+++ b/Examples/UIExplorer/UIExplorerApp.js
@@ -2,6 +2,7 @@
  * Copyright 2004-present Facebook. All Rights Reserved.
  *
  * @providesModule UIExplorerApp
+ * @flow
  */
 'use strict';
 
diff --git a/Examples/UIExplorer/UIExplorerBlock.js b/Examples/UIExplorer/UIExplorerBlock.js
index 4c96ce86d5..007c67afb8 100644
--- a/Examples/UIExplorer/UIExplorerBlock.js
+++ b/Examples/UIExplorer/UIExplorerBlock.js
@@ -2,6 +2,7 @@
  * Copyright 2004-present Facebook. All Rights Reserved.
  *
  * @providesModule UIExplorerBlock
+ * @flow
  */
 'use strict';
 
@@ -19,7 +20,7 @@ var UIExplorerBlock = React.createClass({
   },
 
   getInitialState: function() {
-    return {description: null};
+    return {description: (null: ?string)};
   },
 
   render: function() {
diff --git a/Examples/UIExplorer/UIExplorerList.js b/Examples/UIExplorer/UIExplorerList.js
index 5ca5254ec4..4640cecb2d 100644
--- a/Examples/UIExplorer/UIExplorerList.js
+++ b/Examples/UIExplorer/UIExplorerList.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
diff --git a/Examples/UIExplorer/UIExplorerPage.js b/Examples/UIExplorer/UIExplorerPage.js
index 5d619dcec8..f74a8c7672 100644
--- a/Examples/UIExplorer/UIExplorerPage.js
+++ b/Examples/UIExplorer/UIExplorerPage.js
@@ -2,6 +2,7 @@
  * Copyright 2004-present Facebook. All Rights Reserved.
  *
  * @providesModule UIExplorerPage
+ * @flow
  */
 'use strict';
 
diff --git a/Examples/UIExplorer/UIExplorerTitle.js b/Examples/UIExplorer/UIExplorerTitle.js
index a8fb4ba8dd..2b9b718cb6 100644
--- a/Examples/UIExplorer/UIExplorerTitle.js
+++ b/Examples/UIExplorer/UIExplorerTitle.js
@@ -2,6 +2,7 @@
  * Copyright 2004-present Facebook. All Rights Reserved.
  *
  * @providesModule UIExplorerTitle
+ * @flow
  */
 'use strict';
 
diff --git a/Examples/UIExplorer/VibrationIOSExample.js b/Examples/UIExplorer/VibrationIOSExample.js
index bd768bcbbf..7d69bab2f3 100644
--- a/Examples/UIExplorer/VibrationIOSExample.js
+++ b/Examples/UIExplorer/VibrationIOSExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
diff --git a/Examples/UIExplorer/ViewExample.js b/Examples/UIExplorer/ViewExample.js
index eb2288a493..dbd9bb5c5c 100644
--- a/Examples/UIExplorer/ViewExample.js
+++ b/Examples/UIExplorer/ViewExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
diff --git a/Examples/UIExplorer/WebViewExample.js b/Examples/UIExplorer/WebViewExample.js
index 28246cdc3b..e1a5ee74a6 100644
--- a/Examples/UIExplorer/WebViewExample.js
+++ b/Examples/UIExplorer/WebViewExample.js
@@ -1,5 +1,6 @@
 /**
  * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
  */
 'use strict';
 
@@ -35,6 +36,8 @@ var WebViewExample = React.createClass({
     };
   },
 
+  inputText: '',
+
   handleTextInputChange: function(event) {
     this.inputText = event.nativeEvent.text;
   },
@@ -259,6 +262,6 @@ exports.description = 'Base component to display web content';
 exports.examples = [
   {
     title: 'WebView',
-    render() { return <WebViewExample />; }
+    render(): ReactElement { return <WebViewExample />; }
   }
 ];
diff --git a/Libraries/Components/StatusBar/StatusBarIOS.ios.js b/Libraries/Components/StatusBar/StatusBarIOS.ios.js
index 55cb1608c9..e88f83c23e 100644
--- a/Libraries/Components/StatusBar/StatusBarIOS.ios.js
+++ b/Libraries/Components/StatusBar/StatusBarIOS.ios.js
@@ -21,7 +21,7 @@ var StatusBarIOS = {
     slide: RCTStatusBarManager.Animation.slide,
   },
 
-  setStyle(style: number, animated: boolean) {
+  setStyle(style: number, animated?: boolean) {
     animated = animated || false;
     RCTStatusBarManager.setStyle(style, animated);
   },
diff --git a/Libraries/Utilities/AlertIOS.js b/Libraries/Utilities/AlertIOS.js
index 3b2530f18f..0836bd0871 100644
--- a/Libraries/Utilities/AlertIOS.js
+++ b/Libraries/Utilities/AlertIOS.js
@@ -43,7 +43,7 @@ class AlertIOS {
    */
   static alert(
     title: ?string,
-    message: ?string,
+    message?: ?string,
     buttons?: Array<{
       text: ?string;
       onPress: ?Function;