diff --git a/IntegrationTests/AsyncStorageTest.js b/IntegrationTests/AsyncStorageTest.js
index f3aa7ce8052fe3..42bdbd62965458 100644
--- a/IntegrationTests/AsyncStorageTest.js
+++ b/IntegrationTests/AsyncStorageTest.js
@@ -33,7 +33,7 @@ const VAL_MERGE_EXPECT = {foo: 1, bar: {hoo: 2, boo: 1}, baz: 2, moo: {a: 3}};
 let done = (result: ?boolean) => {};
 let updateMessage = (message: string) => {};
 
-function runTestCase(description: string, fn) {
+function runTestCase(description: string, fn: () => void) {
   updateMessage(description);
   fn();
 }
@@ -61,7 +61,20 @@ function stringify(
   return JSON.stringify(value);
 }
 
-function expectEqual(lhs, rhs, testname: string) {
+function expectEqual(
+  lhs: ?(any | string | Array<Array<string>>),
+  rhs:
+    | null
+    | string
+    | {
+        bar: {boo: number, hoo: number},
+        baz: number,
+        foo: number,
+        moo: {a: number},
+      }
+    | Array<Array<string>>,
+  testname: string,
+) {
   expectTrue(
     !deepDiffer(lhs, rhs),
     'Error in test ' +
@@ -73,7 +86,10 @@ function expectEqual(lhs, rhs, testname: string) {
   );
 }
 
-function expectAsyncNoError(place, err) {
+function expectAsyncNoError(
+  place: string,
+  err: ?(Error | string | Array<Error>),
+) {
   if (err instanceof Error) {
     err = err.message;
   }
diff --git a/Libraries/Alert/Alert.js b/Libraries/Alert/Alert.js
index d05cf9d6be6bb9..f248e2b9055bbe 100644
--- a/Libraries/Alert/Alert.js
+++ b/Libraries/Alert/Alert.js
@@ -105,7 +105,7 @@ class Alert {
           options && options.onDismiss && options.onDismiss();
         }
       };
-      const onError = errorMessage => console.warn(errorMessage);
+      const onError = (errorMessage: string) => console.warn(errorMessage);
       NativeDialogManagerAndroid.showAlert(config, onError, onAction);
     }
   }
diff --git a/Libraries/Animated/AnimatedEvent.js b/Libraries/Animated/AnimatedEvent.js
index 9aa49926152a86..af1d660a8de794 100644
--- a/Libraries/Animated/AnimatedEvent.js
+++ b/Libraries/Animated/AnimatedEvent.js
@@ -41,7 +41,7 @@ function attachNativeEvent(
   // key path inside the `nativeEvent` object. Ex.: ['contentOffset', 'x'].
   const eventMappings = [];
 
-  const traverse = (value, path) => {
+  const traverse = (value: mixed, path: Array<string>) => {
     if (value instanceof AnimatedValue) {
       value.__makeNative(platformConfig);
 
@@ -94,8 +94,8 @@ function attachNativeEvent(
   };
 }
 
-function validateMapping(argMapping, args) {
-  const validate = (recMapping, recEvt, key) => {
+function validateMapping(argMapping: $ReadOnlyArray<?Mapping>, args: any) {
+  const validate = (recMapping: ?Mapping, recEvt: any, key: string) => {
     if (recMapping instanceof AnimatedValue) {
       invariant(
         typeof recEvt === 'number',
@@ -223,7 +223,10 @@ class AnimatedEvent {
         validatedMapping = true;
       }
 
-      const traverse = (recMapping, recEvt) => {
+      const traverse = (
+        recMapping: ?(Mapping | AnimatedValue),
+        recEvt: any,
+      ) => {
         if (recMapping instanceof AnimatedValue) {
           if (typeof recEvt === 'number') {
             recMapping.setValue(recEvt);
diff --git a/Libraries/Animated/AnimatedImplementation.js b/Libraries/Animated/AnimatedImplementation.js
index 84c47e36a1580f..32707208a6ef71 100644
--- a/Libraries/Animated/AnimatedImplementation.js
+++ b/Libraries/Animated/AnimatedImplementation.js
@@ -94,7 +94,7 @@ const _combineCallbacks = function (
   config: $ReadOnly<{...AnimationConfig, ...}>,
 ) {
   if (callback && config.onComplete) {
-    return (...args) => {
+    return (...args: Array<EndResult>) => {
       config.onComplete && config.onComplete(...args);
       callback && callback(...args);
     };
@@ -308,7 +308,7 @@ const sequence = function (
   let current = 0;
   return {
     start: function (callback?: ?EndCallback) {
-      const onComplete = function (result) {
+      const onComplete = function (result: EndResult) {
         if (!result.finished) {
           callback && callback(result);
           return;
@@ -380,7 +380,7 @@ const parallel = function (
       }
 
       animations.forEach((animation, idx) => {
-        const cb = function (endResult) {
+        const cb = function (endResult: EndResult | {finished: boolean}) {
           hasEnded[idx] = true;
           doneCount++;
           if (doneCount === animations.length) {
diff --git a/Libraries/Animated/AnimatedMock.js b/Libraries/Animated/AnimatedMock.js
index af517502197d53..6efb74fd003261 100644
--- a/Libraries/Animated/AnimatedMock.js
+++ b/Libraries/Animated/AnimatedMock.js
@@ -10,6 +10,8 @@
 
 'use strict';
 
+import type {EndResult} from './animations/Animation';
+
 const {AnimatedEvent, attachNativeEvent} = require('./AnimatedEvent');
 const AnimatedImplementation = require('./AnimatedImplementation');
 const AnimatedInterpolation = require('./nodes/AnimatedInterpolation');
@@ -43,7 +45,7 @@ function mockAnimationStart(
     const guardedCallback =
       callback == null
         ? callback
-        : (...args) => {
+        : (...args: Array<EndResult>) => {
             if (inAnimationCallback) {
               console.warn(
                 'Ignoring recursive animation callback when running mock animations',
diff --git a/Libraries/Animated/nodes/AnimatedColor.js b/Libraries/Animated/nodes/AnimatedColor.js
index 8bb31844b22b12..16a87f52800350 100644
--- a/Libraries/Animated/nodes/AnimatedColor.js
+++ b/Libraries/Animated/nodes/AnimatedColor.js
@@ -249,7 +249,7 @@ export default class AnimatedColor extends AnimatedWithChildren {
    */
   addListener(callback: ColorListenerCallback): string {
     const id = String(_uniqueId++);
-    const jointCallback = ({value: number}) => {
+    const jointCallback = ({value: number}: any) => {
       callback(this.__getValue());
     };
     this._listeners[id] = {
diff --git a/Libraries/Animated/nodes/AnimatedValueXY.js b/Libraries/Animated/nodes/AnimatedValueXY.js
index 71d1129c6bcb1f..c54a9d9d6f55e5 100644
--- a/Libraries/Animated/nodes/AnimatedValueXY.js
+++ b/Libraries/Animated/nodes/AnimatedValueXY.js
@@ -177,7 +177,7 @@ class AnimatedValueXY extends AnimatedWithChildren {
    */
   addListener(callback: ValueXYListenerCallback): string {
     const id = String(_uniqueId++);
-    const jointCallback = ({value: number}) => {
+    const jointCallback = ({value: number}: any) => {
       callback(this.__getValue());
     };
     this._listeners[id] = {
diff --git a/Libraries/BatchedBridge/MessageQueue.js b/Libraries/BatchedBridge/MessageQueue.js
index ed32d725da1d27..2ae720810ac9e4 100644
--- a/Libraries/BatchedBridge/MessageQueue.js
+++ b/Libraries/BatchedBridge/MessageQueue.js
@@ -252,7 +252,7 @@ class MessageQueue {
       // folly-convertible.  As a special case, if a prop value is a
       // function it is permitted here, and special-cased in the
       // conversion.
-      const isValidArgument = val => {
+      const isValidArgument = (val: mixed) => {
         switch (typeof val) {
           case 'undefined':
           case 'boolean':
@@ -286,7 +286,7 @@ class MessageQueue {
       // Replacement allows normally non-JSON-convertible values to be
       // seen.  There is ambiguity with string values, but in context,
       // it should at least be a strong hint.
-      const replacer = (key, val) => {
+      const replacer = (key: string, val: $FlowFixMe) => {
         const t = typeof val;
         if (t === 'function') {
           return '<<Function ' + val.name + '>>';
diff --git a/Libraries/Components/ScrollView/ScrollView.js b/Libraries/Components/ScrollView/ScrollView.js
index bc7c06aae7b093..09ef62817f4878 100644
--- a/Libraries/Components/ScrollView/ScrollView.js
+++ b/Libraries/Components/ScrollView/ScrollView.js
@@ -1107,7 +1107,7 @@ class ScrollView extends React.Component<Props, State> {
     }
   };
 
-  _getKeyForIndex(index, childArray) {
+  _getKeyForIndex(index: $FlowFixMe, childArray: $FlowFixMe) {
     const child = childArray[index];
     return child && child.key;
   }
@@ -1140,7 +1140,7 @@ class ScrollView extends React.Component<Props, State> {
     }
   }
 
-  _onStickyHeaderLayout(index, event, key) {
+  _onStickyHeaderLayout(index: $FlowFixMe, event: $FlowFixMe, key: $FlowFixMe) {
     const {stickyHeaderIndices} = this.props;
     if (!stickyHeaderIndices) {
       return;
@@ -1822,7 +1822,7 @@ const styles = StyleSheet.create({
   },
 });
 
-function Wrapper(props, ref) {
+function Wrapper(props, ref: (mixed => mixed) | {current: mixed, ...}) {
   return <ScrollView {...props} scrollViewRef={ref} />;
 }
 Wrapper.displayName = 'ScrollView';
diff --git a/Libraries/Components/Touchable/PooledClass.js b/Libraries/Components/Touchable/PooledClass.js
index 139f1657ea48d3..7a57583a69cb2d 100644
--- a/Libraries/Components/Touchable/PooledClass.js
+++ b/Libraries/Components/Touchable/PooledClass.js
@@ -18,7 +18,7 @@ import invariant from 'invariant';
  * the Class itself, not an instance. If any others are needed, simply add them
  * here, or in their own files.
  */
-const oneArgumentPooler = function (copyFieldsFrom) {
+const oneArgumentPooler = function (copyFieldsFrom: any) {
   const Klass = this; // eslint-disable-line consistent-this
   if (Klass.instancePool.length) {
     const instance = Klass.instancePool.pop();
@@ -29,7 +29,7 @@ const oneArgumentPooler = function (copyFieldsFrom) {
   }
 };
 
-const twoArgumentPooler = function (a1, a2) {
+const twoArgumentPooler = function (a1: any, a2: any) {
   const Klass = this; // eslint-disable-line consistent-this
   if (Klass.instancePool.length) {
     const instance = Klass.instancePool.pop();
@@ -40,7 +40,7 @@ const twoArgumentPooler = function (a1, a2) {
   }
 };
 
-const threeArgumentPooler = function (a1, a2, a3) {
+const threeArgumentPooler = function (a1: any, a2: any, a3: any) {
   const Klass = this; // eslint-disable-line consistent-this
   if (Klass.instancePool.length) {
     const instance = Klass.instancePool.pop();
@@ -51,7 +51,7 @@ const threeArgumentPooler = function (a1, a2, a3) {
   }
 };
 
-const fourArgumentPooler = function (a1, a2, a3, a4) {
+const fourArgumentPooler = function (a1: any, a2: any, a3: any, a4: any) {
   const Klass = this; // eslint-disable-line consistent-this
   if (Klass.instancePool.length) {
     const instance = Klass.instancePool.pop();
diff --git a/Libraries/Components/Touchable/Touchable.js b/Libraries/Components/Touchable/Touchable.js
index 47fdfa892d0662..b4ec927840fe37 100644
--- a/Libraries/Components/Touchable/Touchable.js
+++ b/Libraries/Components/Touchable/Touchable.js
@@ -21,7 +21,18 @@ import type {ColorValue} from '../../StyleSheet/StyleSheet';
 import type {EdgeInsetsProp} from '../../StyleSheet/EdgeInsetsPropType';
 import type {PressEvent} from '../../Types/CoreEventTypes';
 
-const extractSingleTouch = nativeEvent => {
+const extractSingleTouch = (nativeEvent: {
+  +changedTouches: $ReadOnlyArray<PressEvent['nativeEvent']>,
+  +force?: number,
+  +identifier: number,
+  +locationX: number,
+  +locationY: number,
+  +pageX: number,
+  +pageY: number,
+  +target: ?number,
+  +timestamp: number,
+  +touches: $ReadOnlyArray<PressEvent['nativeEvent']>,
+}) => {
   const touches = nativeEvent.touches;
   const changedTouches = nativeEvent.changedTouches;
   const hasTouches = touches && touches.length > 0;
diff --git a/Libraries/Components/Touchable/TouchableNativeFeedback.js b/Libraries/Components/Touchable/TouchableNativeFeedback.js
index 910a51c5e30994..2064a81c36c632 100644
--- a/Libraries/Components/Touchable/TouchableNativeFeedback.js
+++ b/Libraries/Components/Touchable/TouchableNativeFeedback.js
@@ -312,11 +312,11 @@ class TouchableNativeFeedback extends React.Component<Props, State> {
 
 const getBackgroundProp =
   Platform.OS === 'android'
-    ? (background, useForeground) =>
+    ? (background, useForeground: boolean) =>
         useForeground && TouchableNativeFeedback.canUseNativeForeground()
           ? {nativeForegroundAndroid: background}
           : {nativeBackgroundAndroid: background}
-    : (background, useForeground) => null;
+    : (background, useForeground: boolean) => null;
 
 TouchableNativeFeedback.displayName = 'TouchableNativeFeedback';
 
diff --git a/Libraries/Core/Timers/JSTimers.js b/Libraries/Core/Timers/JSTimers.js
index 8682a1dcda572b..2ef47d88c0a6be 100644
--- a/Libraries/Core/Timers/JSTimers.js
+++ b/Libraries/Core/Timers/JSTimers.js
@@ -274,7 +274,7 @@ const JSTimers = {
     const timeout = options && options.timeout;
     const id = _allocateCallback(
       timeout != null
-        ? deadline => {
+        ? (deadline: any) => {
             const timeoutId = requestIdleCallbackTimeouts[id];
             if (timeoutId) {
               JSTimers.clearTimeout(timeoutId);
@@ -364,7 +364,7 @@ const JSTimers = {
         // error one at a time
         for (let ii = 1; ii < errorCount; ii++) {
           JSTimers.setTimeout(
-            (error => {
+            ((error: Error) => {
               throw error;
             }).bind(null, errors[ii]),
             0,
diff --git a/Libraries/Inspector/NetworkOverlay.js b/Libraries/Inspector/NetworkOverlay.js
index a510f357f04697..79f2f301a43c3c 100644
--- a/Libraries/Inspector/NetworkOverlay.js
+++ b/Libraries/Inspector/NetworkOverlay.js
@@ -10,6 +10,8 @@
 
 'use strict';
 
+import type {RenderItemProps} from '../Lists/VirtualizedList';
+
 const ScrollView = require('../Components/ScrollView/ScrollView');
 const TouchableHighlight = require('../Components/Touchable/TouchableHighlight');
 const View = require('../Components/View/View');
@@ -326,7 +328,10 @@ class NetworkOverlay extends React.Component<Props, State> {
     WebSocketInterceptor.disableInterception();
   }
 
-  _renderItem = ({item, index}): React.Element<any> => {
+  _renderItem = ({
+    item,
+    index,
+  }: RenderItemProps<NetworkRequestInfo>): React.Element<any> => {
     const tableRowViewStyle = [
       styles.tableRow,
       index % 2 === 1 ? styles.tableRowOdd : styles.tableRowEven,
@@ -358,7 +363,7 @@ class NetworkOverlay extends React.Component<Props, State> {
     );
   };
 
-  _renderItemDetail(id) {
+  _renderItemDetail(id: number) {
     const requestItem = this.state.requests[id];
     const details = Object.keys(requestItem).map(key => {
       if (key === 'id') {
diff --git a/Libraries/Lists/ViewabilityHelper.js b/Libraries/Lists/ViewabilityHelper.js
index 2e000c8f01ffe1..ae91b25ab68d3b 100644
--- a/Libraries/Lists/ViewabilityHelper.js
+++ b/Libraries/Lists/ViewabilityHelper.js
@@ -259,9 +259,13 @@ class ViewabilityHelper {
   }
 
   _onUpdateSync(
-    viewableIndicesToCheck,
-    onViewableItemsChanged,
-    createViewToken,
+    viewableIndicesToCheck: Array<number>,
+    onViewableItemsChanged: ({
+      changed: Array<ViewToken>,
+      viewableItems: Array<ViewToken>,
+      ...
+    }) => void,
+    createViewToken: (index: number, isViewable: boolean) => ViewToken,
   ) {
     // Filter out indices that have gone out of view since this call was scheduled.
     viewableIndicesToCheck = viewableIndicesToCheck.filter(ii =>
diff --git a/Libraries/Lists/VirtualizedList.js b/Libraries/Lists/VirtualizedList.js
index 685a0269e7eed5..1897a5d3dcb26e 100644
--- a/Libraries/Lists/VirtualizedList.js
+++ b/Libraries/Lists/VirtualizedList.js
@@ -10,7 +10,7 @@
 
 import type {ScrollResponderType} from '../Components/ScrollView/ScrollView';
 import type {ViewStyleProp} from '../StyleSheet/StyleSheet';
-import type {LayoutEvent} from '../Types/CoreEventTypes';
+import type {LayoutEvent, ScrollEvent} from '../Types/CoreEventTypes';
 import type {
   ViewabilityConfig,
   ViewabilityConfigCallbackPair,
@@ -1713,7 +1713,7 @@ class VirtualizedList extends React.PureComponent<Props, State> {
     }
   }
 
-  _onScrollBeginDrag = (e): void => {
+  _onScrollBeginDrag = (e: ScrollEvent): void => {
     this._nestedChildLists.forEach(childList => {
       childList.ref && childList.ref._onScrollBeginDrag(e);
     });
@@ -1724,7 +1724,7 @@ class VirtualizedList extends React.PureComponent<Props, State> {
     this.props.onScrollBeginDrag && this.props.onScrollBeginDrag(e);
   };
 
-  _onScrollEndDrag = (e): void => {
+  _onScrollEndDrag = (e: ScrollEvent): void => {
     this._nestedChildLists.forEach(childList => {
       childList.ref && childList.ref._onScrollEndDrag(e);
     });
@@ -1736,14 +1736,14 @@ class VirtualizedList extends React.PureComponent<Props, State> {
     this.props.onScrollEndDrag && this.props.onScrollEndDrag(e);
   };
 
-  _onMomentumScrollBegin = (e): void => {
+  _onMomentumScrollBegin = (e: ScrollEvent): void => {
     this._nestedChildLists.forEach(childList => {
       childList.ref && childList.ref._onMomentumScrollBegin(e);
     });
     this.props.onMomentumScrollBegin && this.props.onMomentumScrollBegin(e);
   };
 
-  _onMomentumScrollEnd = (e): void => {
+  _onMomentumScrollEnd = (e: ScrollEvent): void => {
     this._nestedChildLists.forEach(childList => {
       childList.ref && childList.ref._onMomentumScrollEnd(e);
     });
@@ -2033,7 +2033,12 @@ class CellRenderer extends React.Component<
       );
   };
 
-  _renderElement(renderItem, ListItemComponent, item, index) {
+  _renderElement(
+    renderItem: any,
+    ListItemComponent: any,
+    item: any,
+    index: any,
+  ) {
     if (renderItem && ListItemComponent) {
       console.warn(
         'VirtualizedList: Both ListItemComponent and renderItem props are present. ListItemComponent will take' +
diff --git a/Libraries/Lists/VirtualizedSectionList.js b/Libraries/Lists/VirtualizedSectionList.js
index 396ad7b58ca2de..f17d6e992a5506 100644
--- a/Libraries/Lists/VirtualizedSectionList.js
+++ b/Libraries/Lists/VirtualizedSectionList.js
@@ -392,21 +392,24 @@ class VirtualizedSectionList<
       }
     };
 
-  _updatePropsFor = (cellKey, value) => {
+  _updatePropsFor = (cellKey: string, value: any) => {
     const updateProps = this._updatePropsMap[cellKey];
     if (updateProps != null) {
       updateProps(value);
     }
   };
 
-  _updateHighlightFor = (cellKey, value) => {
+  _updateHighlightFor = (cellKey: string, value: boolean) => {
     const updateHighlight = this._updateHighlightMap[cellKey];
     if (updateHighlight != null) {
       updateHighlight(value);
     }
   };
 
-  _setUpdateHighlightFor = (cellKey, updateHighlightFn) => {
+  _setUpdateHighlightFor = (
+    cellKey: string,
+    updateHighlightFn: ?(boolean) => void,
+  ) => {
     if (updateHighlightFn != null) {
       this._updateHighlightMap[cellKey] = updateHighlightFn;
     } else {
@@ -414,7 +417,7 @@ class VirtualizedSectionList<
     }
   };
 
-  _setUpdatePropsFor = (cellKey, updatePropsFn) => {
+  _setUpdatePropsFor = (cellKey: string, updatePropsFn: ?(boolean) => void) => {
     if (updatePropsFn != null) {
       this._updatePropsMap[cellKey] = updatePropsFn;
     } else {
@@ -449,7 +452,7 @@ class VirtualizedSectionList<
   _updateHighlightMap: {[string]: (boolean) => void} = {};
   _updatePropsMap: {[string]: void | (boolean => void)} = {};
   _listRef: ?React.ElementRef<typeof VirtualizedList>;
-  _captureRef = ref => {
+  _captureRef = (ref: null | React$ElementRef<Class<VirtualizedList>>) => {
     this._listRef = ref;
   };
 }
diff --git a/Libraries/LogBox/Data/LogBoxData.js b/Libraries/LogBox/Data/LogBoxData.js
index 77b13401823a80..1fb9d59bbec138 100644
--- a/Libraries/LogBox/Data/LogBoxData.js
+++ b/Libraries/LogBox/Data/LogBoxData.js
@@ -133,7 +133,7 @@ function handleUpdate(): void {
   }
 }
 
-function appendNewLog(newLog) {
+function appendNewLog(newLog: LogBoxLog) {
   // Don't want store these logs because they trigger a
   // state update when we add them to the store.
   if (isMessageIgnored(newLog.message.content)) {
diff --git a/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js b/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js
index e683cea4a3ee5b..bd26449ba0a96d 100644
--- a/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js
+++ b/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js
@@ -49,7 +49,7 @@ function getLogBoxSymbolication(): {|
   return (require('../LogBoxSymbolication'): any);
 }
 
-const createStack = methodNames =>
+const createStack = (methodNames: Array<string>) =>
   methodNames.map(methodName => ({
     column: null,
     file: 'file://path/to/file.js',
diff --git a/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js b/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js
index 8c16348598cb64..1d35a1e9867ffd 100644
--- a/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js
+++ b/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js
@@ -22,7 +22,7 @@ const symbolicateStackTrace: JestMockFn<
   Promise<Array<StackFrame>>,
 > = (require('../../../Core/Devtools/symbolicateStackTrace'): any);
 
-const createStack = methodNames =>
+const createStack = (methodNames: Array<string>) =>
   methodNames.map(methodName => ({
     column: null,
     file: 'file://path/to/file.js',
diff --git a/Libraries/LogBox/UI/LogBoxInspectorStackFrames.js b/Libraries/LogBox/UI/LogBoxInspectorStackFrames.js
index b1227d9a6836a1..08eec15d11f441 100644
--- a/Libraries/LogBox/UI/LogBoxInspectorStackFrames.js
+++ b/Libraries/LogBox/UI/LogBoxInspectorStackFrames.js
@@ -8,6 +8,10 @@
  * @format
  */
 
+import type {StackFrame} from '../../Core/NativeExceptionsManager';
+import type {Stack} from '../Data/LogBoxSymbolication';
+import type LogBoxLog from '../Data/LogBoxLog';
+
 import * as React from 'react';
 import StyleSheet from '../../StyleSheet/StyleSheet';
 import Text from '../../Text/Text';
@@ -18,8 +22,6 @@ import LogBoxInspectorStackFrame from './LogBoxInspectorStackFrame';
 import LogBoxInspectorSection from './LogBoxInspectorSection';
 import * as LogBoxStyle from './LogBoxStyle';
 import openFileInEditor from '../../Core/Devtools/openFileInEditor';
-import type {Stack} from '../Data/LogBoxSymbolication';
-import type LogBoxLog from '../Data/LogBoxLog';
 
 type Props = $ReadOnly<{|
   log: LogBoxLog,
@@ -111,7 +113,10 @@ function LogBoxInspectorStackFrames(props: Props): React.Node {
   );
 }
 
-function StackFrameList(props) {
+function StackFrameList(props: {
+  list: Stack | Array<StackFrame>,
+  status: string | 'COMPLETE' | 'FAILED' | 'NONE' | 'PENDING',
+}) {
   return (
     <>
       {props.list.map((frame, index) => {
diff --git a/Libraries/NativeComponent/__tests__/StaticViewConfigValidator-test.js b/Libraries/NativeComponent/__tests__/StaticViewConfigValidator-test.js
index d39afe9f416da6..28b471938c7709 100644
--- a/Libraries/NativeComponent/__tests__/StaticViewConfigValidator-test.js
+++ b/Libraries/NativeComponent/__tests__/StaticViewConfigValidator-test.js
@@ -210,10 +210,10 @@ StaticViewConfigValidator: Invalid static view config for 'RCTView'.
 });
 
 function expectSVCToNotMatchNVC(
-  name,
+  name: string,
   nativeViewConfig,
   staticViewConfig,
-  message,
+  message: string,
 ) {
   const validationResult = StaticViewConfigValidator.validate(
     name,
diff --git a/Libraries/Pressability/Pressability.js b/Libraries/Pressability/Pressability.js
index 4f70f006cf45ce..54b80e5b0c7eaf 100644
--- a/Libraries/Pressability/Pressability.js
+++ b/Libraries/Pressability/Pressability.js
@@ -255,20 +255,20 @@ const Transitions = Object.freeze({
   },
 });
 
-const isActiveSignal = signal =>
+const isActiveSignal = (signal: TouchState) =>
   signal === 'RESPONDER_ACTIVE_PRESS_IN' ||
   signal === 'RESPONDER_ACTIVE_LONG_PRESS_IN';
 
-const isActivationSignal = signal =>
+const isActivationSignal = (signal: TouchState) =>
   signal === 'RESPONDER_ACTIVE_PRESS_OUT' ||
   signal === 'RESPONDER_ACTIVE_PRESS_IN';
 
-const isPressInSignal = signal =>
+const isPressInSignal = (signal: TouchState) =>
   signal === 'RESPONDER_INACTIVE_PRESS_IN' ||
   signal === 'RESPONDER_ACTIVE_PRESS_IN' ||
   signal === 'RESPONDER_ACTIVE_LONG_PRESS_IN';
 
-const isTerminalSignal = signal =>
+const isTerminalSignal = (signal: TouchSignal) =>
   signal === 'RESPONDER_TERMINATED' || signal === 'RESPONDER_RELEASE';
 
 const DEFAULT_LONG_PRESS_DELAY_MS = 500;
@@ -808,7 +808,14 @@ export default class Pressability {
     }
   }
 
-  _measureCallback = (left, top, width, height, pageX, pageY) => {
+  _measureCallback = (
+    left: number,
+    top: number,
+    width: number,
+    height: number,
+    pageX: number,
+    pageY: number,
+  ) => {
     if (!left && !top && !width && !height && !pageX && !pageY) {
       return;
     }
@@ -918,7 +925,11 @@ export default class Pressability {
   }
 }
 
-function normalizeDelay(delay: ?number, min = 0, fallback = 0): number {
+function normalizeDelay(
+  delay: ?number,
+  min: number = 0,
+  fallback: number = 0,
+): number {
   return Math.max(min, delay ?? fallback);
 }
 
diff --git a/Libraries/Pressability/__tests__/Pressability-test.js b/Libraries/Pressability/__tests__/Pressability-test.js
index cbb48e1acf8eb2..42af85f3dff36b 100644
--- a/Libraries/Pressability/__tests__/Pressability-test.js
+++ b/Libraries/Pressability/__tests__/Pressability-test.js
@@ -105,7 +105,7 @@ const mockUIManagerMeasure = (options?: {|delay: number|}) => {
   });
 };
 
-const createMockTargetEvent = registrationName => {
+const createMockTargetEvent = (registrationName: string) => {
   const nativeEvent = {
     target: 42,
   };
@@ -132,7 +132,7 @@ const createMockTargetEvent = registrationName => {
   };
 };
 
-const createMockMouseEvent = registrationName => {
+const createMockMouseEvent = (registrationName: string) => {
   const nativeEvent = {
     clientX: 0,
     clientY: 0,
diff --git a/Libraries/ReactNative/PaperUIManager.js b/Libraries/ReactNative/PaperUIManager.js
index ad83e6248af1f6..b331ca2e95212c 100644
--- a/Libraries/ReactNative/PaperUIManager.js
+++ b/Libraries/ReactNative/PaperUIManager.js
@@ -114,7 +114,7 @@ const UIManagerJS = {
 // $FlowFixMe[prop-missing]
 NativeUIManager.getViewManagerConfig = UIManagerJS.getViewManagerConfig;
 
-function lazifyViewManagerConfig(viewName) {
+function lazifyViewManagerConfig(viewName: string) {
   const viewConfig = getConstants()[viewName];
   viewManagerConfigs[viewName] = viewConfig;
   if (viewConfig.Manager) {
diff --git a/Libraries/Text/Text.js b/Libraries/Text/Text.js
index eafa5e3b277d43..57b6a2ea82ca28 100644
--- a/Libraries/Text/Text.js
+++ b/Libraries/Text/Text.js
@@ -8,6 +8,8 @@
  * @format
  */
 
+import type {PressEvent} from '../Types/CoreEventTypes';
+
 import Platform from '../Utilities/Platform';
 import * as PressabilityDebug from '../Pressability/PressabilityDebug';
 import usePressability from '../Pressability/usePressability';
@@ -73,11 +75,11 @@ const Text: React.AbstractComponent<
             pressRectOffset: pressRetentionOffset,
             onLongPress,
             onPress,
-            onPressIn(event) {
+            onPressIn(event: PressEvent) {
               setHighlighted(!suppressHighlighting);
               onPressIn?.(event);
             },
-            onPressOut(event) {
+            onPressOut(event: PressEvent) {
               setHighlighted(false);
               onPressOut?.(event);
             },
@@ -106,25 +108,25 @@ const Text: React.AbstractComponent<
       eventHandlers == null
         ? null
         : {
-            onResponderGrant(event) {
+            onResponderGrant(event: PressEvent) {
               eventHandlers.onResponderGrant(event);
               if (onResponderGrant != null) {
                 onResponderGrant(event);
               }
             },
-            onResponderMove(event) {
+            onResponderMove(event: PressEvent) {
               eventHandlers.onResponderMove(event);
               if (onResponderMove != null) {
                 onResponderMove(event);
               }
             },
-            onResponderRelease(event) {
+            onResponderRelease(event: PressEvent) {
               eventHandlers.onResponderRelease(event);
               if (onResponderRelease != null) {
                 onResponderRelease(event);
               }
             },
-            onResponderTerminate(event) {
+            onResponderTerminate(event: PressEvent) {
               eventHandlers.onResponderTerminate(event);
               if (onResponderTerminate != null) {
                 onResponderTerminate(event);
diff --git a/Libraries/Utilities/HMRClient.js b/Libraries/Utilities/HMRClient.js
index 63da957ef37028..16870e57071128 100644
--- a/Libraries/Utilities/HMRClient.js
+++ b/Libraries/Utilities/HMRClient.js
@@ -256,7 +256,7 @@ Error: ${e.message}`;
   },
 };
 
-function setHMRUnavailableReason(reason) {
+function setHMRUnavailableReason(reason: string) {
   invariant(hmrClient, 'Expected HMRClient.setup() call at startup.');
   if (hmrUnavailableReason !== null) {
     // Don't show more than one warning.
@@ -273,7 +273,7 @@ function setHMRUnavailableReason(reason) {
   }
 }
 
-function registerBundleEntryPoints(client) {
+function registerBundleEntryPoints(client: MetroHMRClient) {
   if (hmrUnavailableReason != null) {
     DevSettings.reload('Bundle Splitting – Metro disconnected');
     return;
@@ -290,7 +290,7 @@ function registerBundleEntryPoints(client) {
   }
 }
 
-function flushEarlyLogs(client) {
+function flushEarlyLogs(client: MetroHMRClient) {
   try {
     pendingLogs.forEach(([level, data]) => {
       HMRClient.log(level, data);
diff --git a/Libraries/Utilities/ReactNativeTestTools.js b/Libraries/Utilities/ReactNativeTestTools.js
index 4c7bc91b419d47..dfbb46780bc0a5 100644
--- a/Libraries/Utilities/ReactNativeTestTools.js
+++ b/Libraries/Utilities/ReactNativeTestTools.js
@@ -180,7 +180,9 @@ function renderAndEnforceStrictMode(element: React.Node): any {
 }
 
 function renderWithStrictMode(element: React.Node): ReactTestRendererType {
-  const WorkAroundBugWithStrictModeInTestRenderer = prps => prps.children;
+  const WorkAroundBugWithStrictModeInTestRenderer = (prps: {
+    children: React.Node,
+  }) => prps.children;
   const StrictMode = (React: $FlowFixMe).StrictMode;
   return ReactTestRenderer.create(
     <WorkAroundBugWithStrictModeInTestRenderer>
diff --git a/Libraries/Vibration/Vibration.js b/Libraries/Vibration/Vibration.js
index 840527de0de416..f862235d79ef58 100644
--- a/Libraries/Vibration/Vibration.js
+++ b/Libraries/Vibration/Vibration.js
@@ -40,7 +40,7 @@ function vibrateByPattern(pattern: Array<number>, repeat: boolean = false) {
 }
 
 function vibrateScheduler(
-  id,
+  id: number,
   pattern: Array<number>,
   repeat: boolean,
   nextIndex: number,
diff --git a/ReactAndroid/src/androidTest/js/ScrollViewTestModule.js b/ReactAndroid/src/androidTest/js/ScrollViewTestModule.js
index c0c1969a7379a9..50a8b3c8bfa36f 100644
--- a/ReactAndroid/src/androidTest/js/ScrollViewTestModule.js
+++ b/ReactAndroid/src/androidTest/js/ScrollViewTestModule.js
@@ -10,6 +10,11 @@
 
 'use strict';
 
+import type {
+  PressEvent,
+  ScrollEvent,
+} from 'react-native/Libraries/Types/CoreEventTypes';
+
 const BatchedBridge = require('react-native/Libraries/BatchedBridge/BatchedBridge');
 const React = require('react');
 
@@ -26,8 +31,6 @@ const {ScrollListener} = NativeModules;
 
 const NUM_ITEMS = 100;
 
-import type {PressEvent} from 'react-native/Libraries/Types/CoreEventTypes';
-
 // Shared by integration tests for ScrollView and HorizontalScrollView
 
 let scrollViewApp: ScrollViewTestApp | HorizontalScrollViewTestApp;
@@ -61,28 +64,28 @@ const getInitialState = function () {
   };
 };
 
-const onScroll = function (e) {
+const onScroll = function (e: ScrollEvent) {
   ScrollListener.onScroll(
     e.nativeEvent.contentOffset.x,
     e.nativeEvent.contentOffset.y,
   );
 };
 
-const onScrollBeginDrag = function (e) {
+const onScrollBeginDrag = function (e: ScrollEvent) {
   ScrollListener.onScrollBeginDrag(
     e.nativeEvent.contentOffset.x,
     e.nativeEvent.contentOffset.y,
   );
 };
 
-const onScrollEndDrag = function (e) {
+const onScrollEndDrag = function (e: ScrollEvent) {
   ScrollListener.onScrollEndDrag(
     e.nativeEvent.contentOffset.x,
     e.nativeEvent.contentOffset.y,
   );
 };
 
-const onItemPress = function (itemNumber) {
+const onItemPress = function (itemNumber: number) {
   ScrollListener.onItemPress(itemNumber);
 };
 
diff --git a/ReactCommon/hermes/inspector/tools/msggen/src/HeaderWriter.js b/ReactCommon/hermes/inspector/tools/msggen/src/HeaderWriter.js
index b8f5cdb32e8a61..5784f9f2f261bd 100644
--- a/ReactCommon/hermes/inspector/tools/msggen/src/HeaderWriter.js
+++ b/ReactCommon/hermes/inspector/tools/msggen/src/HeaderWriter.js
@@ -70,7 +70,7 @@ export class HeaderWriter {
     this.stream.write('struct UnknownRequest;\n\n');
 
     const namespaceMap: Map<string, Array<Type | Command | Event>> = new Map();
-    const addToMap = function (type) {
+    const addToMap = function (type: Type | Command | Event) {
       const domain = type.domain;
       let types = namespaceMap.get(domain);
       if (!types) {
diff --git a/ReactCommon/hermes/inspector/tools/msggen/src/index.js b/ReactCommon/hermes/inspector/tools/msggen/src/index.js
index eb9a4f3ba96501..1a137ac7170759 100644
--- a/ReactCommon/hermes/inspector/tools/msggen/src/index.js
+++ b/ReactCommon/hermes/inspector/tools/msggen/src/index.js
@@ -32,7 +32,7 @@ type Descriptor = {|
   events: Array<Event>,
 |};
 
-function mergeDomains(original, extra) {
+function mergeDomains(original: any, extra: any) {
   return {...original, domains: original.domains.concat(extra.domains)};
 }
 
@@ -186,7 +186,7 @@ function filterReachableFromRoots(
 
   // Sort commands and events so the code is easier to read. Types have to be
   // topologically sorted as explained above.
-  const comparator = (a, b) => {
+  const comparator = (a: Command | Event, b: Command | Event) => {
     const id1 = a.getDebuggerName();
     const id2 = b.getDebuggerName();
     return id1 < id2 ? -1 : id1 > id2 ? 1 : 0;
diff --git a/packages/react-native-codegen/src/generators/RNCodegen.js b/packages/react-native-codegen/src/generators/RNCodegen.js
index dd9cd1283958cc..78004999db3a0b 100644
--- a/packages/react-native-codegen/src/generators/RNCodegen.js
+++ b/packages/react-native-codegen/src/generators/RNCodegen.js
@@ -198,7 +198,7 @@ module.exports = {
   ): boolean {
     schemaValidator.validate(schema);
 
-    function composePath(intermediate) {
+    function composePath(intermediate: string) {
       return path.join(outputDirectory, intermediate, libraryName);
     }
 
diff --git a/packages/react-native-codegen/src/generators/components/CppHelpers.js b/packages/react-native-codegen/src/generators/components/CppHelpers.js
index 92ee6c2529b1d0..608fd6d98127a5 100644
--- a/packages/react-native-codegen/src/generators/components/CppHelpers.js
+++ b/packages/react-native-codegen/src/generators/components/CppHelpers.js
@@ -57,7 +57,13 @@ function getImports(
 ): Set<string> {
   const imports: Set<string> = new Set();
 
-  function addImportsForNativeName(name) {
+  function addImportsForNativeName(
+    name:
+      | 'ColorPrimitive'
+      | 'EdgeInsetsPrimitive'
+      | 'ImageSourcePrimitive'
+      | 'PointPrimitive',
+  ) {
     switch (name) {
       case 'ColorPrimitive':
         return;
diff --git a/packages/react-native-codegen/src/generators/components/GenerateEventEmitterCpp.js b/packages/react-native-codegen/src/generators/components/GenerateEventEmitterCpp.js
index 59690c61e6e48e..cb82e3903b0663 100644
--- a/packages/react-native-codegen/src/generators/components/GenerateEventEmitterCpp.js
+++ b/packages/react-native-codegen/src/generators/components/GenerateEventEmitterCpp.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {EventTypeShape} from '../../CodegenSchema';
 
 const {generateEventStructName} = require('./CppHelpers.js');
 
@@ -90,7 +91,11 @@ void ${className}EventEmitter::${eventName}() const {
 }
 `.trim();
 
-function generateSetter(variableName, propertyName, propertyParts) {
+function generateSetter(
+  variableName: string,
+  propertyName: string,
+  propertyParts: $ReadOnlyArray<string>,
+) {
   const trailingPeriod = propertyParts.length === 0 ? '' : '.';
   const eventChain = `event.${propertyParts.join(
     '.',
@@ -99,7 +104,11 @@ function generateSetter(variableName, propertyName, propertyParts) {
   return `${variableName}.setProperty(runtime, "${propertyName}", ${eventChain}`;
 }
 
-function generateEnumSetter(variableName, propertyName, propertyParts) {
+function generateEnumSetter(
+  variableName: string,
+  propertyName: string,
+  propertyParts: $ReadOnlyArray<string>,
+) {
   const trailingPeriod = propertyParts.length === 0 ? '' : '.';
   const eventChain = `event.${propertyParts.join(
     '.',
@@ -177,7 +186,7 @@ function generateSetters(
   return propSetters;
 }
 
-function generateEvent(componentName: string, event): string {
+function generateEvent(componentName: string, event: EventTypeShape): string {
   // This is a gross hack necessary because native code is sending
   // events named things like topChange to JS which is then converted back to
   // call the onChange prop. We should be consistent throughout the system.
diff --git a/packages/react-native-codegen/src/generators/components/GenerateEventEmitterH.js b/packages/react-native-codegen/src/generators/components/GenerateEventEmitterH.js
index 8eba4d79f6ab2c..269567575c02f0 100644
--- a/packages/react-native-codegen/src/generators/components/GenerateEventEmitterH.js
+++ b/packages/react-native-codegen/src/generators/components/GenerateEventEmitterH.js
@@ -135,7 +135,11 @@ function getNativeTypeFromAnnotation(
       throw new Error(`Received invalid event property type ${type}`);
   }
 }
-function generateEnum(structs, options, nameParts) {
+function generateEnum(
+  structs: StructsMap,
+  options: $ReadOnlyArray<string>,
+  nameParts: Array<string>,
+) {
   const structName = generateEventStructName(nameParts);
   const fields = options
     .map((option, index) => `${toSafeCppString(option)}`)
@@ -218,7 +222,10 @@ function generateStruct(
   );
 }
 
-function generateStructs(componentName: string, component): string {
+function generateStructs(
+  componentName: string,
+  component: ComponentShape,
+): string {
   const structs: StructsMap = new Map();
 
   component.events.forEach(event => {
@@ -244,7 +251,10 @@ function generateEvent(componentName: string, event: EventTypeShape): string {
 
   return `void ${event.name}() const;`;
 }
-function generateEvents(componentName: string, component): string {
+function generateEvents(
+  componentName: string,
+  component: ComponentShape,
+): string {
   return component.events
     .map(event => generateEvent(componentName, event))
     .join('\n\n' + '  ');
diff --git a/packages/react-native-codegen/src/generators/components/GeneratePropsCpp.js b/packages/react-native-codegen/src/generators/components/GeneratePropsCpp.js
index 145b8467757ae7..ad9d6aac61f45a 100644
--- a/packages/react-native-codegen/src/generators/components/GeneratePropsCpp.js
+++ b/packages/react-native-codegen/src/generators/components/GeneratePropsCpp.js
@@ -74,7 +74,7 @@ function generatePropsString(componentName: string, component: ComponentShape) {
     .join(',\n' + '    ');
 }
 
-function getClassExtendString(component): string {
+function getClassExtendString(component: ComponentShape): string {
   const extendString =
     ' ' +
     component.extendsProps
diff --git a/packages/react-native-codegen/src/generators/components/GeneratePropsH.js b/packages/react-native-codegen/src/generators/components/GeneratePropsH.js
index fc8202a1c09e7e..26521b0cbb1936 100644
--- a/packages/react-native-codegen/src/generators/components/GeneratePropsH.js
+++ b/packages/react-native-codegen/src/generators/components/GeneratePropsH.js
@@ -9,6 +9,16 @@
  */
 
 'use strict';
+import type {
+  StringTypeAnnotation,
+  ReservedPropTypeAnnotation,
+  ObjectTypeAnnotation,
+  Int32TypeAnnotation,
+  FloatTypeAnnotation,
+  DoubleTypeAnnotation,
+  ComponentShape,
+  BooleanTypeAnnotation,
+} from '../../CodegenSchema';
 
 const {
   convertDefaultTypeToString,
@@ -257,7 +267,7 @@ static inline std::string toString(const ${enumMask} &value) {
 }
 `.trim();
 
-function getClassExtendString(component): string {
+function getClassExtendString(component: ComponentShape): string {
   if (component.extendsProps.length === 0) {
     throw new Error('Invalid: component.extendsProps is empty');
   }
@@ -286,7 +296,29 @@ function getClassExtendString(component): string {
 
 function getNativeTypeFromAnnotation(
   componentName: string,
-  prop,
+  prop:
+    | NamedShape<PropTypeAnnotation>
+    | {
+        name: string,
+        typeAnnotation:
+          | $FlowFixMe
+          | DoubleTypeAnnotation
+          | FloatTypeAnnotation
+          | BooleanTypeAnnotation
+          | Int32TypeAnnotation
+          | StringTypeAnnotation
+          | ObjectTypeAnnotation<PropTypeAnnotation>
+          | ReservedPropTypeAnnotation
+          | {
+              +default: string,
+              +options: $ReadOnlyArray<string>,
+              +type: 'StringEnumTypeAnnotation',
+            }
+          | {
+              +elementType: ObjectTypeAnnotation<PropTypeAnnotation>,
+              +type: 'ArrayTypeAnnotation',
+            },
+      },
   nameParts: $ReadOnlyArray<string>,
 ): string {
   const typeAnnotation = prop.typeAnnotation;
@@ -400,7 +432,10 @@ function generateArrayEnumString(
   });
 }
 
-function generateStringEnum(componentName, prop) {
+function generateStringEnum(
+  componentName: string,
+  prop: NamedShape<PropTypeAnnotation>,
+) {
   const typeAnnotation = prop.typeAnnotation;
   if (typeAnnotation.type === 'StringEnumTypeAnnotation') {
     const values: $ReadOnlyArray<string> = typeAnnotation.options;
@@ -435,7 +470,10 @@ function generateStringEnum(componentName, prop) {
   return '';
 }
 
-function generateIntEnum(componentName, prop) {
+function generateIntEnum(
+  componentName: string,
+  prop: NamedShape<PropTypeAnnotation>,
+) {
   const typeAnnotation = prop.typeAnnotation;
   if (typeAnnotation.type === 'Int32EnumTypeAnnotation') {
     const values: $ReadOnlyArray<number> = typeAnnotation.options;
@@ -476,7 +514,10 @@ function generateIntEnum(componentName, prop) {
   return '';
 }
 
-function generateEnumString(componentName: string, component): string {
+function generateEnumString(
+  componentName: string,
+  component: ComponentShape,
+): string {
   return component.props
     .map(prop => {
       if (
@@ -567,7 +608,13 @@ function getLocalImports(
 ): Set<string> {
   const imports: Set<string> = new Set();
 
-  function addImportsForNativeName(name) {
+  function addImportsForNativeName(
+    name:
+      | 'ColorPrimitive'
+      | 'EdgeInsetsPrimitive'
+      | 'ImageSourcePrimitive'
+      | 'PointPrimitive',
+  ) {
     switch (name) {
       case 'ColorPrimitive':
         imports.add('#include <react/renderer/graphics/Color.h>');
@@ -635,7 +682,10 @@ function getLocalImports(
   return imports;
 }
 
-function generateStructsForComponent(componentName: string, component): string {
+function generateStructsForComponent(
+  componentName: string,
+  component: ComponentShape,
+): string {
   const structs = generateStructs(componentName, component.props, []);
   const structArray = Array.from(structs.values());
   if (structArray.length < 1) {
@@ -646,8 +696,8 @@ function generateStructsForComponent(componentName: string, component): string {
 
 function generateStructs(
   componentName: string,
-  properties,
-  nameParts,
+  properties: $ReadOnlyArray<NamedShape<PropTypeAnnotation>>,
+  nameParts: Array<string>,
 ): StructsMap {
   const structs: StructsMap = new Map();
   properties.forEach(prop => {
diff --git a/packages/react-native-codegen/src/generators/components/GeneratePropsJavaDelegate.js b/packages/react-native-codegen/src/generators/components/GeneratePropsJavaDelegate.js
index 17bdbda66ad175..f39fe2a51d9055 100644
--- a/packages/react-native-codegen/src/generators/components/GeneratePropsJavaDelegate.js
+++ b/packages/react-native-codegen/src/generators/components/GeneratePropsJavaDelegate.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {CommandParamTypeAnnotation} from '../../CodegenSchema';
 
 import type {
   NamedShape,
@@ -170,7 +171,10 @@ function generatePropCasesString(
     }`;
 }
 
-function getCommandArgJavaType(param, index) {
+function getCommandArgJavaType(
+  param: NamedShape<CommandParamTypeAnnotation>,
+  index: number,
+) {
   const {typeAnnotation} = param;
 
   switch (typeAnnotation.type) {
@@ -229,7 +233,7 @@ function generateCommandCasesString(
   return commandMethods;
 }
 
-function getClassExtendString(component): string {
+function getClassExtendString(component: ComponentShape): string {
   const extendString = component.extendsProps
     .map(extendProps => {
       switch (extendProps.type) {
@@ -251,7 +255,7 @@ function getClassExtendString(component): string {
   return extendString;
 }
 
-function getDelegateImports(component) {
+function getDelegateImports(component: ComponentShape) {
   const imports = getImports(component, 'delegate');
   // The delegate needs ReadableArray for commands always.
   // The interface doesn't always need it
@@ -265,7 +269,10 @@ function getDelegateImports(component) {
   return imports;
 }
 
-function generateMethods(propsString, commandsString): string {
+function generateMethods(
+  propsString: string,
+  commandsString: null | string,
+): string {
   return [
     PropSetterTemplate({propCases: propsString}),
     commandsString != null
diff --git a/packages/react-native-codegen/src/generators/components/GeneratePropsJavaInterface.js b/packages/react-native-codegen/src/generators/components/GeneratePropsJavaInterface.js
index 581564d10fc08c..5afeeb6e51db10 100644
--- a/packages/react-native-codegen/src/generators/components/GeneratePropsJavaInterface.js
+++ b/packages/react-native-codegen/src/generators/components/GeneratePropsJavaInterface.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {CommandParamTypeAnnotation} from '../../CodegenSchema';
 
 import type {
   NamedShape,
@@ -56,13 +57,13 @@ public interface ${className}<T extends ${extendClasses}> {
 }
 `;
 
-function addNullable(imports) {
+function addNullable(imports: Set<string>) {
   imports.add('import androidx.annotation.Nullable;');
 }
 
 function getJavaValueForProp(
   prop: NamedShape<PropTypeAnnotation>,
-  imports,
+  imports: Set<string>,
 ): string {
   const typeAnnotation = prop.typeAnnotation;
 
@@ -126,7 +127,7 @@ function getJavaValueForProp(
   }
 }
 
-function generatePropsString(component: ComponentShape, imports) {
+function generatePropsString(component: ComponentShape, imports: Set<string>) {
   if (component.props.length === 0) {
     return '// No props';
   }
@@ -140,7 +141,7 @@ function generatePropsString(component: ComponentShape, imports) {
     .join('\n' + '  ');
 }
 
-function getCommandArgJavaType(param) {
+function getCommandArgJavaType(param: NamedShape<CommandParamTypeAnnotation>) {
   const {typeAnnotation} = param;
 
   switch (typeAnnotation.type) {
@@ -198,7 +199,7 @@ function generateCommandsString(
     .join('\n' + '  ');
 }
 
-function getClassExtendString(component): string {
+function getClassExtendString(component: ComponentShape): string {
   const extendString = component.extendsProps
     .map(extendProps => {
       switch (extendProps.type) {
diff --git a/packages/react-native-codegen/src/generators/components/GenerateTests.js b/packages/react-native-codegen/src/generators/components/GenerateTests.js
index dbaffefdd7217c..cfefaa318bd946 100644
--- a/packages/react-native-codegen/src/generators/components/GenerateTests.js
+++ b/packages/react-native-codegen/src/generators/components/GenerateTests.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {PropTypeAnnotation, ComponentShape} from '../../CodegenSchema';
 
 import type {SchemaType} from '../../CodegenSchema';
 const {getImports, toSafeCppString} = require('./CppHelpers');
@@ -76,7 +77,10 @@ TEST(${componentName}_${testName}, etc) {
 }
 `;
 
-function getTestCasesForProp(propName, typeAnnotation) {
+function getTestCasesForProp(
+  propName: string,
+  typeAnnotation: PropTypeAnnotation,
+) {
   const cases = [];
   if (typeAnnotation.type === 'StringEnumTypeAnnotation') {
     typeAnnotation.options.forEach(option =>
@@ -134,7 +138,7 @@ function getTestCasesForProp(propName, typeAnnotation) {
   return cases;
 }
 
-function generateTestsString(name, component) {
+function generateTestsString(name: string, component: ComponentShape) {
   function createTest({testName, propName, propValue, raw = false}: TestCase) {
     const value =
       !raw && typeof propValue === 'string' ? `"${propValue}"` : propValue;
diff --git a/packages/react-native-codegen/src/generators/modules/GenerateModuleCpp.js b/packages/react-native-codegen/src/generators/modules/GenerateModuleCpp.js
index 5d7d481383b44a..046e86b1c65e0a 100644
--- a/packages/react-native-codegen/src/generators/modules/GenerateModuleCpp.js
+++ b/packages/react-native-codegen/src/generators/modules/GenerateModuleCpp.js
@@ -127,7 +127,7 @@ function serializeArg(
     realTypeAnnotation = resolveAlias(realTypeAnnotation.name);
   }
 
-  function wrap(callback) {
+  function wrap(callback: (val: string) => string) {
     const val = `args[${index}]`;
     const expression = callback(val);
 
diff --git a/packages/react-native-codegen/src/generators/modules/GenerateModuleH.js b/packages/react-native-codegen/src/generators/modules/GenerateModuleH.js
index d21f33c928355c..1f518d3f47e0f9 100644
--- a/packages/react-native-codegen/src/generators/modules/GenerateModuleH.js
+++ b/packages/react-native-codegen/src/generators/modules/GenerateModuleH.js
@@ -119,7 +119,7 @@ function translatePrimitiveJSTypeToCpp(
     realTypeAnnotation = resolveAlias(realTypeAnnotation.name);
   }
 
-  function wrap(type) {
+  function wrap(type: string) {
     return nullable ? `std::optional<${type}>` : type;
   }
 
diff --git a/packages/react-native-codegen/src/parsers/flow/components/props.js b/packages/react-native-codegen/src/parsers/flow/components/props.js
index 1c7982da781226..003f47bed2e29e 100644
--- a/packages/react-native-codegen/src/parsers/flow/components/props.js
+++ b/packages/react-native-codegen/src/parsers/flow/components/props.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {ASTNode} from '../utils';
 
 const {getValueFromTypes} = require('../utils.js');
 
@@ -177,7 +178,7 @@ function getTypeAnnotationForArray(
 
 function getTypeAnnotation(
   name: string,
-  annotation,
+  annotation: $FlowFixMe | ASTNode,
   defaultValue: $FlowFixMe | null,
   withNullDefault: boolean,
   types: TypeDeclarationMap,
diff --git a/packages/react-native-codegen/src/parsers/flow/modules/__tests__/module-parser-e2e-test.js b/packages/react-native-codegen/src/parsers/flow/modules/__tests__/module-parser-e2e-test.js
index 2601d945f74821..25c9d178d7d0ac 100644
--- a/packages/react-native-codegen/src/parsers/flow/modules/__tests__/module-parser-e2e-test.js
+++ b/packages/react-native-codegen/src/parsers/flow/modules/__tests__/module-parser-e2e-test.js
@@ -712,7 +712,7 @@ describe('Flow Module Parser', () => {
       const RETURN_TYPE_DESCRIPTION = IS_RETURN_TYPE_NULLABLE
         ? 'a nullable'
         : 'a non-nullable';
-      const annotateRet = retType =>
+      const annotateRet = (retType: string) =>
         IS_RETURN_TYPE_NULLABLE ? `?${retType}` : retType;
 
       function parseReturnType(
@@ -927,7 +927,7 @@ describe('Flow Module Parser', () => {
                   ? 'an optional'
                   : 'a required';
 
-              function annotateProp(propName, propType) {
+              function annotateProp(propName: string, propType: string) {
                 if (nullable && optional) {
                   return `${propName}?: ?${propType}`;
                 }
@@ -1229,7 +1229,7 @@ describe('Flow Module Parser', () => {
   });
 });
 
-function parseModule(source) {
+function parseModule(source: string) {
   const schema = parseString(source, `${MODULE_NAME}.js`);
   const module = schema.modules.NativeFoo;
   invariant(
diff --git a/packages/react-native-codegen/src/parsers/flow/modules/index.js b/packages/react-native-codegen/src/parsers/flow/modules/index.js
index 10153679a65767..38ce80db4e746c 100644
--- a/packages/react-native-codegen/src/parsers/flow/modules/index.js
+++ b/packages/react-native-codegen/src/parsers/flow/modules/index.js
@@ -549,7 +549,7 @@ function buildPropertySchema(
   };
 }
 
-function isModuleInterface(node) {
+function isModuleInterface(node: $FlowFixMe) {
   return (
     node.type === 'InterfaceDeclaration' &&
     node.extends.length === 1 &&
diff --git a/packages/react-native-codegen/src/parsers/typescript/components/props.js b/packages/react-native-codegen/src/parsers/typescript/components/props.js
index 68d1d85e0b3891..1d58f0d2445ada 100644
--- a/packages/react-native-codegen/src/parsers/typescript/components/props.js
+++ b/packages/react-native-codegen/src/parsers/typescript/components/props.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {ASTNode} from '../utils';
 
 const {getValueFromTypes} = require('../utils.js');
 
@@ -221,7 +222,7 @@ function getTypeAnnotationForArray(
 
 function getTypeAnnotation(
   name: string,
-  annotation,
+  annotation: $FlowFixMe | ASTNode,
   defaultValue: $FlowFixMe | null,
   withNullDefault: boolean,
   types: TypeDeclarationMap,
diff --git a/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/typescript-module-parser-e2e-test.js b/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/typescript-module-parser-e2e-test.js
index caa2043ca55cb5..99b7702f5fd640 100644
--- a/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/typescript-module-parser-e2e-test.js
+++ b/packages/react-native-codegen/src/parsers/typescript/modules/__tests__/typescript-module-parser-e2e-test.js
@@ -714,7 +714,7 @@ describe('TypeScript Module Parser', () => {
       const RETURN_TYPE_DESCRIPTION = IS_RETURN_TYPE_NULLABLE
         ? 'a nullable'
         : 'a non-nullable';
-      const annotateRet = retType =>
+      const annotateRet = (retType: string) =>
         IS_RETURN_TYPE_NULLABLE ? `${retType} | null | void` : retType;
 
       function parseReturnType(
@@ -927,7 +927,7 @@ describe('TypeScript Module Parser', () => {
                   ? 'an optional'
                   : 'a required';
 
-              function annotateProp(propName, propType) {
+              function annotateProp(propName: string, propType: string) {
                 if (nullable && optional) {
                   return `${propName}?: ${propType} | null | void`;
                 }
@@ -1231,7 +1231,7 @@ describe('TypeScript Module Parser', () => {
   });
 });
 
-function parseModule(source) {
+function parseModule(source: string) {
   const schema = parseString(source, `${MODULE_NAME}.ts`);
   const module = schema.modules.NativeFoo;
   invariant(
diff --git a/packages/react-native-codegen/src/parsers/typescript/modules/index.js b/packages/react-native-codegen/src/parsers/typescript/modules/index.js
index 66041f980dfa91..a2048bbdc822d3 100644
--- a/packages/react-native-codegen/src/parsers/typescript/modules/index.js
+++ b/packages/react-native-codegen/src/parsers/typescript/modules/index.js
@@ -551,7 +551,7 @@ function buildPropertySchema(
   };
 }
 
-function isModuleInterface(node) {
+function isModuleInterface(node: $FlowFixMe) {
   return (
     node.type === 'TSInterfaceDeclaration' &&
     node.extends.length === 1 &&
diff --git a/packages/rn-tester/js/examples/AnimatedGratuitousApp/AnExApp.js b/packages/rn-tester/js/examples/AnimatedGratuitousApp/AnExApp.js
index 171c61b2b0c85b..3788016c810b1a 100644
--- a/packages/rn-tester/js/examples/AnimatedGratuitousApp/AnExApp.js
+++ b/packages/rn-tester/js/examples/AnimatedGratuitousApp/AnExApp.js
@@ -189,7 +189,7 @@ class Circle extends React.Component<any, any> {
       </Animated.View>
     );
   }
-  _toggleIsActive = velocity => {
+  _toggleIsActive = (velocity: void) => {
     const config = {tension: 30, friction: 7};
     if (this.state.isActive) {
       Animated.spring(this.props.openVal, {
@@ -311,7 +311,7 @@ function distance(p1: Point, p2: Point): number {
   return dx * dx + dy * dy;
 }
 
-function moveToClosest({activeKey, keys, restLayouts}, position) {
+function moveToClosest({activeKey, keys, restLayouts}: any, position: Point) {
   const activeIdx = -1;
   let closestIdx = activeIdx;
   let minDist = Infinity;
diff --git a/packages/rn-tester/js/examples/Button/ButtonExample.js b/packages/rn-tester/js/examples/Button/ButtonExample.js
index dd97ad5a78f414..cc04f1e0bea7cf 100644
--- a/packages/rn-tester/js/examples/Button/ButtonExample.js
+++ b/packages/rn-tester/js/examples/Button/ButtonExample.js
@@ -15,7 +15,7 @@ const React = require('react');
 const {Alert, Button, View, StyleSheet} = require('react-native');
 const {RNTesterThemeContext} = require('../../components/RNTesterTheme');
 
-function onButtonPress(buttonName) {
+function onButtonPress(buttonName: string) {
   Alert.alert(`Your application has been ${buttonName}!`);
 }
 
diff --git a/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js b/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js
index 4faee1f310ab1c..6e8eb5f8851a38 100644
--- a/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js
+++ b/packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestResultView.js
@@ -8,6 +8,7 @@
  * @flow
  */
 
+import type {RenderItemProps} from 'react-native/Libraries/Lists/VirtualizedList';
 import type {
   ViewStyleProp,
   TextStyle,
@@ -73,7 +74,7 @@ const TableRow = React.memo(
   },
 );
 
-function renderTableRow({item}) {
+function renderTableRow({item}: RenderItemProps<PlatformTestResult>) {
   return <TableRow testResult={item} />;
 }
 
diff --git a/packages/rn-tester/js/examples/Experimental/W3CPointerEventPlatformTests/PointerEventSupport.js b/packages/rn-tester/js/examples/Experimental/W3CPointerEventPlatformTests/PointerEventSupport.js
index 99208285875479..0fa7ceb46b5bb2 100644
--- a/packages/rn-tester/js/examples/Experimental/W3CPointerEventPlatformTests/PointerEventSupport.js
+++ b/packages/rn-tester/js/examples/Experimental/W3CPointerEventPlatformTests/PointerEventSupport.js
@@ -60,19 +60,19 @@ export function check_PointerEvent(
   // * if the attribute is "readonly", it cannot be changed
   // TA: 1.1, 1.2
   const idl_type_check = {
-    long: function (v) {
+    long: function (v: any) {
       return typeof v === 'number' && Math.round(v) === v;
     },
-    float: function (v) {
+    float: function (v: any) {
       return typeof v === 'number';
     },
-    string: function (v) {
+    string: function (v: any) {
       return typeof v === 'string';
     },
-    boolean: function (v) {
+    boolean: function (v: any) {
       return typeof v === 'boolean';
     },
-    object: function (v) {
+    object: function (v: any) {
       return typeof v === 'object';
     },
   };
@@ -189,7 +189,8 @@ export function useTestEventHandler(
   handler: (event: any, eventName: string) => void,
 ): ViewProps {
   const eventProps: any = useMemo(() => {
-    const handlerFactory = eventName => event => handler(event, eventName);
+    const handlerFactory = (eventName: string) => (event: any) =>
+      handler(event, eventName);
     const props = {};
     for (const eventName of eventNames) {
       const eventPropName =
diff --git a/packages/rn-tester/js/examples/Experimental/W3CPointerEventsExample.js b/packages/rn-tester/js/examples/Experimental/W3CPointerEventsExample.js
index 5cf7c0e865018e..d105decc169c62 100644
--- a/packages/rn-tester/js/examples/Experimental/W3CPointerEventsExample.js
+++ b/packages/rn-tester/js/examples/Experimental/W3CPointerEventsExample.js
@@ -8,6 +8,7 @@
  * @flow
  */
 
+import type {PointerEvent} from 'react-native/Libraries/Types/CoreEventTypes';
 import {Button, StyleSheet, ScrollView, View, Text} from 'react-native';
 import * as React from 'react';
 import type {ViewProps} from 'react-native/Libraries/Components/View/ViewPropTypes';
@@ -55,7 +56,7 @@ function EventfulView(props: {|
   } = props;
   const [tag, setTag] = React.useState('');
 
-  const eventLog = eventName => event => {
+  const eventLog = (eventName: string) => (event: PointerEvent) => {
     // $FlowFixMe Using private property
     log(`${name} - ${eventName} - target: ${event.target._nativeTag}`);
   };
@@ -159,7 +160,7 @@ function PointerEventScaffolding({
 }) {
   const [eventsLog, setEventsLog] = React.useState('');
   const clear = () => setEventsLog('');
-  const log = eventStr => {
+  const log = (eventStr: string) => {
     setEventsLog(currentEventsLog => `${eventStr}\n${currentEventsLog}`);
   };
   return (
diff --git a/packages/rn-tester/js/examples/FlatList/FlatList-onEndReached.js b/packages/rn-tester/js/examples/FlatList/FlatList-onEndReached.js
index c2b206020a7f6b..7d5c0437d3ea16 100644
--- a/packages/rn-tester/js/examples/FlatList/FlatList-onEndReached.js
+++ b/packages/rn-tester/js/examples/FlatList/FlatList-onEndReached.js
@@ -16,7 +16,8 @@ import * as React from 'react';
 export function FlatList_onEndReached(): React.Node {
   const [output, setOutput] = React.useState('');
   const exampleProps = {
-    onEndReached: info => setOutput('onEndReached'),
+    onEndReached: (info: {distanceFromEnd: number, ...}) =>
+      setOutput('onEndReached'),
     onEndReachedThreshold: 0,
   };
   const ref = React.useRef(null);
diff --git a/packages/rn-tester/js/examples/FlatList/FlatList-withSeparators.js b/packages/rn-tester/js/examples/FlatList/FlatList-withSeparators.js
index b73288462980c3..9a0f0294891f9e 100644
--- a/packages/rn-tester/js/examples/FlatList/FlatList-withSeparators.js
+++ b/packages/rn-tester/js/examples/FlatList/FlatList-withSeparators.js
@@ -15,8 +15,13 @@ import {StyleSheet, View, Text} from 'react-native';
 import * as React from 'react';
 
 const Separator =
-  (defaultColor, highlightColor) =>
-  ({leadingItem, trailingItem, highlighted, hasBeenHighlighted}) => {
+  (defaultColor: string, highlightColor: string) =>
+  ({
+    leadingItem,
+    trailingItem,
+    highlighted,
+    hasBeenHighlighted,
+  }: $FlowFixMe) => {
     const text = `Separator for leading ${leadingItem} and trailing ${trailingItem} has ${
       !hasBeenHighlighted ? 'not ' : ''
     }been pressed`;
diff --git a/packages/rn-tester/js/examples/Image/ImageExample.js b/packages/rn-tester/js/examples/Image/ImageExample.js
index c1c4ef96bffaa2..eacc26ec27500e 100644
--- a/packages/rn-tester/js/examples/Image/ImageExample.js
+++ b/packages/rn-tester/js/examples/Image/ImageExample.js
@@ -10,6 +10,8 @@
 
 'use strict';
 
+import type {LayoutEvent} from 'react-native/Libraries/Types/CoreEventTypes';
+
 const React = require('react');
 
 const {
@@ -451,7 +453,7 @@ class OnLayoutExample extends React.Component<
     layoutHandlerMessage: 'No Message',
   };
 
-  onLayoutHandler = event => {
+  onLayoutHandler = (event: LayoutEvent) => {
     this.setState({
       width: this.state.width,
       height: this.state.height,
diff --git a/packages/rn-tester/js/examples/KeyboardAvoidingView/KeyboardAvoidingViewExample.js b/packages/rn-tester/js/examples/KeyboardAvoidingView/KeyboardAvoidingViewExample.js
index 627b5751f7522c..7a86ed1d872df8 100644
--- a/packages/rn-tester/js/examples/KeyboardAvoidingView/KeyboardAvoidingViewExample.js
+++ b/packages/rn-tester/js/examples/KeyboardAvoidingView/KeyboardAvoidingViewExample.js
@@ -42,7 +42,11 @@ const TextInputForm = () => {
   );
 };
 
-const CloseButton = props => {
+const CloseButton = (
+  props:
+    | {behavior: any, setModalOpen: any}
+    | {behavior: string, setModalOpen: any},
+) => {
   return (
     <View
       style={[
diff --git a/packages/rn-tester/js/examples/NativeAnimation/NativeAnimationsExample.js b/packages/rn-tester/js/examples/NativeAnimation/NativeAnimationsExample.js
index 131430910878b3..c5dabd8589cb15 100644
--- a/packages/rn-tester/js/examples/NativeAnimation/NativeAnimationsExample.js
+++ b/packages/rn-tester/js/examples/NativeAnimation/NativeAnimationsExample.js
@@ -10,6 +10,8 @@
 
 'use strict';
 
+import type AnimatedValue from 'react-native/Libraries/Animated/nodes/AnimatedValue';
+
 const React = require('react');
 
 const {
@@ -313,7 +315,7 @@ class TrackingExample extends React.Component<
     this.state.toJS.setValue(nextValue);
   };
 
-  renderBlock = (anim, dest) => [
+  renderBlock = (anim: any | AnimatedValue, dest: any | AnimatedValue) => [
     <Animated.View
       key="line"
       style={[styles.line, {transform: [{translateX: dest}]}]}
diff --git a/packages/rn-tester/js/examples/PointerEvents/PointerEventsExample.js b/packages/rn-tester/js/examples/PointerEvents/PointerEventsExample.js
index 22e4f04777953d..57654c0687bfdf 100644
--- a/packages/rn-tester/js/examples/PointerEvents/PointerEventsExample.js
+++ b/packages/rn-tester/js/examples/PointerEvents/PointerEventsExample.js
@@ -268,7 +268,7 @@ const exampleClasses: Array<ExampleClass> = [
   },
 ];
 
-const infoToExample = info => {
+const infoToExample = (info: ExampleClass) => {
   return {
     title: info.title,
     description: info.description,
diff --git a/packages/rn-tester/js/examples/Pressable/PressableExample.js b/packages/rn-tester/js/examples/Pressable/PressableExample.js
index f4629a8bb290c4..b13987f1246586 100644
--- a/packages/rn-tester/js/examples/Pressable/PressableExample.js
+++ b/packages/rn-tester/js/examples/Pressable/PressableExample.js
@@ -84,7 +84,7 @@ function TextOnPressBox() {
 function PressableFeedbackEvents() {
   const [eventLog, setEventLog] = useState([]);
 
-  function appendEvent(eventName) {
+  function appendEvent(eventName: string) {
     const limit = 6;
     setEventLog(current => {
       return [eventName].concat(current.slice(0, limit - 1));
@@ -120,7 +120,7 @@ function PressableFeedbackEvents() {
 function PressableDelayEvents() {
   const [eventLog, setEventLog] = useState([]);
 
-  function appendEvent(eventName) {
+  function appendEvent(eventName: string) {
     const limit = 6;
     const newEventLog = eventLog.slice(0, limit - 1);
     newEventLog.unshift(eventName);
diff --git a/packages/rn-tester/js/examples/RTL/RTLExample.js b/packages/rn-tester/js/examples/RTL/RTLExample.js
index 25415fe0c302ea..f9bb40b4b3a83f 100644
--- a/packages/rn-tester/js/examples/RTL/RTLExample.js
+++ b/packages/rn-tester/js/examples/RTL/RTLExample.js
@@ -43,7 +43,7 @@ const IMAGE_SIZE = [IMAGE_DIMENSION, IMAGE_DIMENSION];
 
 const IS_RTL = I18nManager.isRTL;
 
-function ListItem(props) {
+function ListItem(props: {imageSource: number}) {
   return (
     <View style={styles.row}>
       <View style={styles.column1}>
@@ -127,7 +127,10 @@ const IconsExample = withRTLState(({isRTL, setRTL}) => {
   );
 });
 
-function AnimationBlock(props) {
+function AnimationBlock(props: {
+  imgStyle: {transform: Array<{scaleX: number} | {translateX: any}>},
+  onPress: (e: any) => void,
+}) {
   return (
     <View style={styles.block}>
       <TouchableWithoutFeedback onPress={props.onPress}>
@@ -144,7 +147,13 @@ type RTLSwitcherComponentState = {|
   isRTL: boolean,
 |};
 
-function withRTLState(Component) {
+function withRTLState(
+  Component: ({
+    isRTL: boolean,
+    setRTL: (isRTL: boolean) => void,
+    style?: any,
+  }) => React.Node,
+) {
   return class extends React.Component<
     {style?: any},
     RTLSwitcherComponentState,
@@ -157,7 +166,7 @@ function withRTLState(Component) {
     }
 
     render() {
-      const setRTL = isRTL => this.setState({isRTL: isRTL});
+      const setRTL = (isRTL: boolean) => this.setState({isRTL: isRTL});
       return (
         <Component isRTL={this.state.isRTL} setRTL={setRTL} {...this.props} />
       );
@@ -165,7 +174,12 @@ function withRTLState(Component) {
   };
 }
 
-const RTLToggler = ({isRTL, setRTL}) => {
+const RTLToggler = ({
+  isRTL,
+  setRTL,
+}:
+  | {isRTL: any, setRTL: any}
+  | {isRTL: boolean, setRTL: (isRTL: boolean) => void}) => {
   if (Platform.OS === 'android') {
     return <Text style={styles.rtlToggler}>{isRTL ? 'RTL' : 'LTR'}</Text>;
   }
@@ -528,7 +542,7 @@ const BorderExample = withRTLState(({isRTL, setRTL}) => {
   );
 });
 
-const directionStyle = isRTL =>
+const directionStyle = (isRTL: boolean) =>
   Platform.OS !== 'android' ? {direction: isRTL ? 'rtl' : 'ltr'} : null;
 
 const styles = StyleSheet.create({
diff --git a/packages/rn-tester/js/examples/SafeAreaView/SafeAreaViewExample.js b/packages/rn-tester/js/examples/SafeAreaView/SafeAreaViewExample.js
index ad75dac32b7bbc..12268f6edee774 100644
--- a/packages/rn-tester/js/examples/SafeAreaView/SafeAreaViewExample.js
+++ b/packages/rn-tester/js/examples/SafeAreaView/SafeAreaViewExample.js
@@ -32,7 +32,7 @@ class SafeAreaViewExample extends React.Component<
     modalVisible: false,
   };
 
-  _setModalVisible = visible => {
+  _setModalVisible = (visible: boolean) => {
     this.setState({modalVisible: visible});
   };
 
diff --git a/packages/rn-tester/js/examples/ScrollView/ScrollViewExample.js b/packages/rn-tester/js/examples/ScrollView/ScrollViewExample.js
index e86361950f21b5..499a077e863560 100644
--- a/packages/rn-tester/js/examples/ScrollView/ScrollViewExample.js
+++ b/packages/rn-tester/js/examples/ScrollView/ScrollViewExample.js
@@ -732,7 +732,7 @@ const RefreshControlExample = () => {
     wait(2000).then(() => setRefreshing(false));
   }, []);
 
-  const wait = timeout => {
+  const wait = (timeout: number) => {
     return new Promise(resolve => {
       setTimeout(resolve, timeout);
     });
@@ -1253,7 +1253,9 @@ class Item extends React.PureComponent<{|
 
 let ITEMS = [...Array(12)].map((_, i) => `Item ${i}`);
 
-const createItemRow = (msg, index) => <Item key={index} msg={msg} />;
+const createItemRow = (msg: string, index: number) => (
+  <Item key={index} msg={msg} />
+);
 
 const Button = (props: {
   active?: boolean,
diff --git a/packages/rn-tester/js/examples/SectionList/SectionList-onEndReached.js b/packages/rn-tester/js/examples/SectionList/SectionList-onEndReached.js
index 04c5dc6ea46c80..498f0c4e8d98aa 100644
--- a/packages/rn-tester/js/examples/SectionList/SectionList-onEndReached.js
+++ b/packages/rn-tester/js/examples/SectionList/SectionList-onEndReached.js
@@ -14,7 +14,8 @@ import * as React from 'react';
 export function SectionList_onEndReached(): React.Node {
   const [output, setOutput] = React.useState('');
   const exampleProps = {
-    onEndReached: info => setOutput('onEndReached'),
+    onEndReached: (info: {distanceFromEnd: number, ...}) =>
+      setOutput('onEndReached'),
     onEndReachedThreshold: 0,
   };
   const ref = React.useRef(null);
diff --git a/packages/rn-tester/js/examples/SectionList/SectionList-onViewableItemsChanged.js b/packages/rn-tester/js/examples/SectionList/SectionList-onViewableItemsChanged.js
index ff40342e58751a..f93996530880ba 100644
--- a/packages/rn-tester/js/examples/SectionList/SectionList-onViewableItemsChanged.js
+++ b/packages/rn-tester/js/examples/SectionList/SectionList-onViewableItemsChanged.js
@@ -8,6 +8,7 @@
  * @flow
  */
 
+import type {ViewToken} from 'react-native/Libraries/Lists/ViewabilityHelper';
 import SectionListBaseExample from './SectionListBaseExample';
 import {View, StyleSheet, SectionList} from 'react-native';
 import * as React from 'react';
@@ -30,7 +31,11 @@ export function SectionList_onViewableItemsChanged(props: {
   const {viewabilityConfig, offScreen, horizontal, useScrollRefScroll} = props;
   const [output, setOutput] = React.useState('');
   const exampleProps = {
-    onViewableItemsChanged: info =>
+    onViewableItemsChanged: (info: {
+      changed: Array<ViewToken>,
+      viewableItems: Array<ViewToken>,
+      ...
+    }) =>
       setOutput(
         info.viewableItems
           .filter(viewToken => viewToken.index != null && viewToken.isViewable)
diff --git a/packages/rn-tester/js/examples/SectionList/SectionList-scrollable.js b/packages/rn-tester/js/examples/SectionList/SectionList-scrollable.js
index 88fda4e8171869..58452b7badc0a9 100644
--- a/packages/rn-tester/js/examples/SectionList/SectionList-scrollable.js
+++ b/packages/rn-tester/js/examples/SectionList/SectionList-scrollable.js
@@ -9,6 +9,7 @@
  */
 
 'use strict';
+import type {Item} from '../../components/ListExampleShared';
 const RNTesterPage = require('../../components/RNTesterPage');
 const React = require('react');
 
@@ -108,7 +109,7 @@ const EmptySectionList = () => (
 );
 
 const renderItemComponent =
-  setItemState =>
+  (setItemState: (item: Item) => void) =>
   ({item, separators}) => {
     if (isNaN(item.key)) {
       return;
@@ -164,7 +165,7 @@ export function SectionList_scrollable(Props: {
   const [data, setData] = React.useState(genItemData(1000));
 
   const filterRegex = new RegExp(String(filterText), 'i');
-  const filter = item =>
+  const filter = (item: Item) =>
     filterRegex.test(item.text) || filterRegex.test(item.title);
   const filteredData = data.filter(filter);
   const filteredSectionData = [...CONSTANT_SECTION_EXAMPLES];
@@ -181,7 +182,7 @@ export function SectionList_scrollable(Props: {
     startIndex = ii;
   }
 
-  const setItemPress = item => {
+  const setItemPress = (item: Item) => {
     if (isNaN(item.key)) {
       return;
     }
@@ -190,7 +191,7 @@ export function SectionList_scrollable(Props: {
   };
 
   const ref = React.useRef<?React.ElementRef<typeof SectionList>>(null);
-  const scrollToLocation = (sectionIndex, itemIndex) => {
+  const scrollToLocation = (sectionIndex: number, itemIndex: number) => {
     // $FlowFixMe[method-unbinding] added when improving typing for this parameters
     if (ref != null && ref.current?.scrollToLocation != null) {
       ref.current.scrollToLocation({sectionIndex, itemIndex});
diff --git a/packages/rn-tester/js/examples/SectionList/SectionList-withSeparators.js b/packages/rn-tester/js/examples/SectionList/SectionList-withSeparators.js
index ec93af1f63b991..9042f205d334e8 100644
--- a/packages/rn-tester/js/examples/SectionList/SectionList-withSeparators.js
+++ b/packages/rn-tester/js/examples/SectionList/SectionList-withSeparators.js
@@ -13,8 +13,8 @@ import {View, Text, StyleSheet} from 'react-native';
 import * as React from 'react';
 
 const Separator =
-  (defaultColor, highlightColor, isSectionSeparator) =>
-  ({leadingItem, trailingItem, highlighted, hasBeenHighlighted}) => {
+  (defaultColor: string, highlightColor: string, isSectionSeparator: boolean) =>
+  ({leadingItem, trailingItem, highlighted, hasBeenHighlighted}: any) => {
     const text = `${
       isSectionSeparator ? 'Section ' : ''
     }separator for leading ${leadingItem} and trailing ${trailingItem} has ${
diff --git a/packages/rn-tester/js/examples/SwipeableCardExample/SwipeableCardExample.js b/packages/rn-tester/js/examples/SwipeableCardExample/SwipeableCardExample.js
index fe7c947e9094d0..41ff93ac454bc0 100644
--- a/packages/rn-tester/js/examples/SwipeableCardExample/SwipeableCardExample.js
+++ b/packages/rn-tester/js/examples/SwipeableCardExample/SwipeableCardExample.js
@@ -8,6 +8,8 @@
  * @format
  */
 
+import type {RenderItemProps} from 'react-native/Libraries/Lists/VirtualizedList';
+
 import * as React from 'react';
 import {
   Animated,
@@ -49,7 +51,7 @@ function SwipeableCardExample() {
 
   const incrementCurrent = () => setCurrentIndex(currentIndex + 1);
 
-  const getCardColor = index => cardColors[index % cardColors.length];
+  const getCardColor = (index: number) => cardColors[index % cardColors.length];
 
   /*
    * The cards try to reuse the views. Instead of always rebuilding the current card on top
@@ -140,7 +142,7 @@ function SwipeableCard(props: {
 const cardData = Array(5);
 
 function Card(props: {color: string}) {
-  const renderItem = ({item, index}) => (
+  const renderItem = ({item, index}: RenderItemProps<$FlowFixMe>) => (
     <CardSection color={props.color} index={index} />
   );
 
diff --git a/packages/rn-tester/js/examples/TextInput/TextInputExample.ios.js b/packages/rn-tester/js/examples/TextInput/TextInputExample.ios.js
index be0a6f60357045..5d27d97eccbc21 100644
--- a/packages/rn-tester/js/examples/TextInput/TextInputExample.ios.js
+++ b/packages/rn-tester/js/examples/TextInput/TextInputExample.ios.js
@@ -46,7 +46,7 @@ class TextInputAccessoryViewChangeTextExample extends React.Component<
   {...},
   {text: string},
 > {
-  constructor(props) {
+  constructor(props: void | {...}) {
     super(props);
     this.state = {text: 'Placeholder Text'};
   }
@@ -79,7 +79,7 @@ class TextInputAccessoryViewChangeKeyboardExample extends React.Component<
   {...},
   {keyboardType: string, text: string},
 > {
-  constructor(props) {
+  constructor(props: void | {...}) {
     super(props);
     this.state = {text: '', keyboardType: 'default'};
   }
@@ -121,7 +121,7 @@ class TextInputAccessoryViewDefaultDoneButtonExample extends React.Component<
   |}>,
   {text: string},
 > {
-  constructor(props) {
+  constructor(props: void | $ReadOnly<{keyboardType: KeyboardType}>) {
     super(props);
     this.state = {text: ''};
   }
@@ -140,7 +140,7 @@ class TextInputAccessoryViewDefaultDoneButtonExample extends React.Component<
 }
 
 class RewriteExampleKana extends React.Component<$FlowFixMeProps, any> {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {text: ''};
   }
@@ -161,7 +161,7 @@ class RewriteExampleKana extends React.Component<$FlowFixMeProps, any> {
 }
 
 class SecureEntryExample extends React.Component<$FlowFixMeProps, any> {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {
       text: '',
@@ -209,7 +209,7 @@ class AutogrowingTextInputExample extends React.Component<
   $FlowFixMeProps,
   $FlowFixMeState,
 > {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
 
     this.state = {
@@ -223,7 +223,7 @@ class AutogrowingTextInputExample extends React.Component<
     };
   }
 
-  UNSAFE_componentWillReceiveProps(props) {
+  UNSAFE_componentWillReceiveProps(props: any) {
     this.setState({
       multiline: props.multiline,
     });
diff --git a/packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js b/packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js
index 19e758f2a7dd5a..24874bf2dac977 100644
--- a/packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js
+++ b/packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js
@@ -88,7 +88,7 @@ class WithLabel extends React.Component<$FlowFixMeProps> {
 }
 
 class RewriteExample extends React.Component<$FlowFixMeProps, any> {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {text: ''};
   }
@@ -122,7 +122,7 @@ class RewriteExampleInvalidCharacters extends React.Component<
   $FlowFixMeProps,
   any,
 > {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {text: ''};
   }
@@ -150,7 +150,7 @@ class RewriteInvalidCharactersAndClearExample extends React.Component<
 > {
   inputRef: ?React.ElementRef<typeof TextInput> = null;
 
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {text: ''};
   }
@@ -248,7 +248,7 @@ class TextEventsExample extends React.Component<{...}, $FlowFixMeState> {
     prev3Text: '<No Event>',
   };
 
-  updateText = text => {
+  updateText = (text: string) => {
     this.setState(state => {
       return {
         curText: text,
@@ -305,7 +305,7 @@ class TokenizedTextExample extends React.Component<
   $FlowFixMeProps,
   $FlowFixMeState,
 > {
-  constructor(props) {
+  constructor(props: any | void) {
     super(props);
     this.state = {text: 'Hello #World'};
   }
@@ -396,7 +396,7 @@ class SelectionExample extends React.Component<
     return Math.round(Math.random() * length);
   }
 
-  select(start, end) {
+  select(start: number, end: number) {
     this._textInput?.focus();
     this.setState({selection: {start, end}});
     if (this.props.imperative) {
@@ -412,7 +412,7 @@ class SelectionExample extends React.Component<
     this.select(...positions);
   }
 
-  placeAt(position) {
+  placeAt(position: number) {
     this.select(position, position);
   }
 
diff --git a/packages/rn-tester/js/examples/Timer/TimerExample.js b/packages/rn-tester/js/examples/Timer/TimerExample.js
index e06b1cd227fcff..2a4b75849fc46c 100644
--- a/packages/rn-tester/js/examples/Timer/TimerExample.js
+++ b/packages/rn-tester/js/examples/Timer/TimerExample.js
@@ -15,7 +15,7 @@ const React = require('react');
 
 const {Alert, Platform, ToastAndroid, Text, View} = require('react-native');
 
-function burnCPU(milliseconds) {
+function burnCPU(milliseconds: number) {
   const start = global.performance.now();
   while (global.performance.now() < start + milliseconds) {}
 }
@@ -117,7 +117,11 @@ class RequestIdleCallbackTester extends React.Component<
       this._idleTimer = null;
     }
 
-    const handler = deadline => {
+    const handler = (deadline: {
+      didTimeout: boolean,
+      timeRemaining: () => number,
+      ...
+    }) => {
       while (deadline.timeRemaining() > 5) {
         burnCPU(5);
         this.setState({
diff --git a/packages/rn-tester/js/examples/Touchable/TouchableExample.js b/packages/rn-tester/js/examples/Touchable/TouchableExample.js
index eed3b4a53a21b3..a4df8b52ada0bd 100644
--- a/packages/rn-tester/js/examples/Touchable/TouchableExample.js
+++ b/packages/rn-tester/js/examples/Touchable/TouchableExample.js
@@ -181,7 +181,7 @@ class TouchableFeedbackEvents extends React.Component<{...}, $FlowFixMeState> {
     );
   }
 
-  _appendEvent = eventName => {
+  _appendEvent = (eventName: string) => {
     const limit = 6;
     const eventLog = this.state.eventLog.slice(0, limit - 1);
     eventLog.unshift(eventName);
@@ -222,7 +222,7 @@ class TouchableDelayEvents extends React.Component<{...}, $FlowFixMeState> {
     );
   }
 
-  _appendEvent = eventName => {
+  _appendEvent = (eventName: string) => {
     const limit = 6;
     const eventLog = this.state.eventLog.slice(0, limit - 1);
     eventLog.unshift(eventName);
diff --git a/packages/rn-tester/js/examples/TurboModule/SampleTurboModuleExample.js b/packages/rn-tester/js/examples/TurboModule/SampleTurboModuleExample.js
index 96c91a34f11449..09e14a94e247f2 100644
--- a/packages/rn-tester/js/examples/TurboModule/SampleTurboModuleExample.js
+++ b/packages/rn-tester/js/examples/TurboModule/SampleTurboModuleExample.js
@@ -73,7 +73,33 @@ class SampleTurboModuleExample extends React.Component<{||}, State> {
       NativeSampleTurboModule.getValue(5, 'test', {a: 1, b: 'foo'}),
   };
 
-  _setResult(name, result) {
+  _setResult(
+    name:
+      | string
+      | 'callback'
+      | 'getArray'
+      | 'getBool'
+      | 'getConstants'
+      | 'getNumber'
+      | 'getObject'
+      | 'getRootTag'
+      | 'getString'
+      | 'getUnsafeObject'
+      | 'getValue'
+      | 'promise'
+      | 'rejectPromise'
+      | 'voidFunc',
+    result:
+      | $FlowFixMe
+      | void
+      | RootTag
+      | Promise<mixed>
+      | number
+      | string
+      | boolean
+      | {const1: boolean, const2: number, const3: string}
+      | Array<$FlowFixMe>,
+  ) {
     this.setState(({testResults}) => ({
       /* $FlowFixMe[cannot-spread-indexer] (>=0.122.0 site=react_native_fb)
        * This comment suppresses an error found when Flow v0.122.0 was
@@ -88,7 +114,22 @@ class SampleTurboModuleExample extends React.Component<{||}, State> {
     }));
   }
 
-  _renderResult(name) {
+  _renderResult(
+    name:
+      | 'callback'
+      | 'getArray'
+      | 'getBool'
+      | 'getConstants'
+      | 'getNumber'
+      | 'getObject'
+      | 'getRootTag'
+      | 'getString'
+      | 'getUnsafeObject'
+      | 'getValue'
+      | 'promise'
+      | 'rejectPromise'
+      | 'voidFunc',
+  ) {
     const result = this.state.testResults[name] || {};
     return (
       <View style={styles.result}>