diff --git a/flow/babel.js.flow b/flow/babel.js.flow
index ad97546cc..bc80b72e8 100644
--- a/flow/babel.js.flow
+++ b/flow/babel.js.flow
@@ -52,7 +52,7 @@ type GeneratorOptions = {
 type InlinePlugin = [string | {} | () => {}, any];
 
 // based on https://babeljs.io/docs/usage/options/ -- 2016-11-11
-type _TransformOptions = {
+type __TransformOptions = {
   filename?: string,
   filenameRelative?: string,
   presets?: Array<string | Object>,
@@ -85,8 +85,8 @@ type _TransformOptions = {
   extends?: string,
 };
 
-type TransformOptions =
-  _TransformOptions & {env?: {[key: string]: TransformOptions}};
+type _TransformOptions =
+  __TransformOptions & {env?: {[key: string]: __TransformOptions}};
 declare class _Ast {};
 type TransformResult = {
   ast: _Ast,
@@ -98,9 +98,10 @@ type VisitFn = <State>(path: Object, state: State) => any;
 declare module 'babel-core' {
   declare type SourceMap = _SourceMap;
   declare type Ast = _Ast;
+  declare type TransformOptions = _TransformOptions;
   declare function transform(
     code: string,
-    options?: TransformOptions,
+    options?: _TransformOptions,
   ): TransformResult;
   declare function traverse<State>(
     ast: _Ast,
@@ -114,7 +115,7 @@ declare module 'babel-core' {
   declare function transformFromAst(
     ast: _Ast,
     code?: ?string,
-    babelOptions?: TransformOptions,
+    babelOptions?: _TransformOptions,
   ): TransformResult;
 }
 
diff --git a/packager/react-packager/src/Bundler/index.js b/packager/react-packager/src/Bundler/index.js
index f7624ad97..e8499574c 100644
--- a/packager/react-packager/src/Bundler/index.js
+++ b/packager/react-packager/src/Bundler/index.js
@@ -35,9 +35,10 @@ const {
   extname,
 } = require('path');
 
-import AssetServer from '../AssetServer';
-import Module from '../node-haste/Module';
-import ResolutionResponse from '../node-haste/DependencyGraph/ResolutionResponse';
+import type AssetServer from '../AssetServer';
+import type Module from '../node-haste/Module';
+import type ResolutionResponse from '../node-haste/DependencyGraph/ResolutionResponse';
+import type {Options as TransformOptions} from '../JSTransformer/worker/worker';
 
 export type GetTransformOptions<T> = (
   string,
@@ -353,8 +354,6 @@ class Bundler {
           ? runBeforeMainModule
               .map(name => modulesByName[name])
               .filter(Boolean)
-              /* $FlowFixMe: looks like ResolutionResponse is monkey-patched
-               * with `getModuleId`. */
               .map(response.getModuleId)
           : undefined;
 
@@ -450,7 +449,8 @@ class Bundler {
           entryFilePath,
           assetPlugins,
           transformOptions: response.transformOptions,
-          getModuleId: response.getModuleId,
+          /* $FlowFixMe: `getModuleId` is monkey-patched */
+          getModuleId: (response.getModuleId: () => number),
           dependencyPairs: response.getResolvedDependencyPairs(module),
         }).then(transformed => {
           modulesByName[transformed.name] = module;
@@ -485,7 +485,7 @@ class Bundler {
     generateSourceMaps = false,
   }: {
     entryFile: string,
-    platform: ?string,
+    platform: string,
     dev?: boolean,
     minify?: boolean,
     hot?: boolean,
@@ -528,14 +528,14 @@ class Bundler {
     onProgress,
   }: {
     entryFile: string,
-    platform: ?string,
+    platform: string,
     dev?: boolean,
     minify?: boolean,
     hot?: boolean,
     recursive?: boolean,
     generateSourceMaps?: boolean,
     isolateModuleIDs?: boolean,
-    onProgress?: () => mixed,
+    onProgress?: ?(finishedModules: number, totalModules: number) => mixed,
   }) {
     return this.getTransformOptions(
       entryFile,
@@ -567,7 +567,7 @@ class Bundler {
   getOrderedDependencyPaths({ entryFile, dev, platform }: {
     entryFile: string,
     dev: boolean,
-    platform: ?string,
+    platform: string,
   }) {
     return this.getDependencies({entryFile, dev, platform}).then(
       ({ dependencies }) => {
@@ -608,7 +608,15 @@ class Bundler {
     getModuleId,
     dependencyPairs,
     assetPlugins,
-  }) {
+  }: {
+    module: Module,
+    bundle: Bundle,
+    entryFilePath: string,
+    transformOptions: TransformOptions,
+    getModuleId: () => number,
+    dependencyPairs: Array<[mixed, {path: string}]>,
+    assetPlugins: Array<string>,
+  }): Promise<ModuleTransport> {
     let moduleTransport;
     const moduleId = getModuleId(module);
 
@@ -670,7 +678,9 @@ class Bundler {
         __packager_asset: true,
         fileSystemLocation: pathDirname(module.path),
         httpServerLocation: assetUrlPath,
+        /* $FlowFixMe: `resolution` is assets-only */
         width: dimensions ? dimensions.width / module.resolution : undefined,
+        /* $FlowFixMe: `resolution` is assets-only */
         height: dimensions ? dimensions.height / module.resolution : undefined,
         scales: assetData.scales,
         files: assetData.files,
@@ -718,9 +728,9 @@ class Bundler {
   }
 
   _generateAssetModule(
-    bundle,
-    module,
-    moduleId,
+    bundle: Bundle,
+    module: Module,
+    moduleId: number,
     assetPlugins: Array<string> = [],
     platform: ?string = null,
   ) {
@@ -745,7 +755,7 @@ class Bundler {
     mainModuleName: string,
     options: {
       dev?: boolean,
-      platform: ?string,
+      platform: string,
       hot?: boolean,
       generateSourceMaps?: boolean,
     },
diff --git a/packager/react-packager/src/JSTransformer/worker/worker.js b/packager/react-packager/src/JSTransformer/worker/worker.js
index 794532188..a81edf9e1 100644
--- a/packager/react-packager/src/JSTransformer/worker/worker.js
+++ b/packager/react-packager/src/JSTransformer/worker/worker.js
@@ -18,7 +18,7 @@ const invariant = require('invariant');
 const minify = require('./minify');
 
 import type {LogEntry} from '../../Logger/Types';
-import type {Ast, SourceMap} from 'babel-core';
+import type {Ast, SourceMap, TransformOptions} from 'babel-core';
 
 function makeTransformParams(filename, sourceCode, options) {
   if (filename.endsWith('.json')) {
@@ -31,7 +31,7 @@ export type TransformedCode = {
   code: string,
   dependencies: Array<string>,
   dependencyOffsets: Array<number>,
-  map?: ?{},
+  map?: ?SourceMap,
 };
 
 type Transform = (
@@ -47,7 +47,13 @@ type Transform = (
 ) => void;
 
 export type Options = {
-  transform?: {projectRoots: Array<string>},
+  transform: {
+    projectRoots: Array<string>,
+    ramGroups: Array<string>,
+    platform: string,
+    preloadedModules: Array<string>,
+  } & TransformOptions,
+  platform: string,
 };
 
 export type Data = {
@@ -132,7 +138,7 @@ exports.transformAndExtractDependencies = (
   transform: string,
   filename: string,
   sourceCode: string,
-  options: ?Options,
+  options: Options,
   callback: Callback,
 ) => {
   /* $FlowFixMe: impossible to type a dynamic require */
diff --git a/packager/react-packager/src/Resolver/index.js b/packager/react-packager/src/Resolver/index.js
index 68fb11883..87e23493a 100644
--- a/packager/react-packager/src/Resolver/index.js
+++ b/packager/react-packager/src/Resolver/index.js
@@ -5,9 +5,11 @@
  * This source code is licensed under the BSD-style license found in the
  * LICENSE file in the root directory of this source tree. An additional grant
  * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
  */
-'use strict';
 
+'use strict';
 
 const DependencyGraph = require('../node-haste');
 
@@ -15,6 +17,11 @@ const declareOpts = require('../lib/declareOpts');
 const defaults = require('../../../defaults');
 const pathJoin = require('path').join;
 
+import type ResolutionResponse from '../node-haste/DependencyGraph/ResolutionResponse';
+import type Module from '../node-haste/Module';
+import type {SourceMap} from '../lib/SourceMap';
+import type {Options as TransformOptions} from '../JSTransformer/worker/worker';
+
 const validateOpts = declareOpts({
   projectRoots: {
     type: 'array',
@@ -87,7 +94,12 @@ const getDependenciesValidateOpts = declareOpts({
 
 class Resolver {
 
-  constructor(options) {
+  _depGraph: DependencyGraph;
+  _minifyCode: (filePath: string, code: string, map: SourceMap) =>
+    Promise<{code: string, map: SourceMap}>;
+  _polyfillModuleNames: Array<string>;
+
+  constructor(options: {resetCache: boolean}) {
     const opts = validateOpts(options);
 
     this._depGraph = new DependencyGraph({
@@ -122,15 +134,24 @@ class Resolver {
     });
   }
 
-  getShallowDependencies(entryFile, transformOptions) {
+  getShallowDependencies(
+    entryFile: string,
+    transformOptions: TransformOptions,
+  ): Array<string> {
     return this._depGraph.getShallowDependencies(entryFile, transformOptions);
   }
 
-  getModuleForPath(entryFile) {
+  getModuleForPath(entryFile: string): Module {
     return this._depGraph.getModuleForPath(entryFile);
   }
 
-  getDependencies(entryPath, options, transformOptions, onProgress, getModuleId) {
+  getDependencies(
+    entryPath: string,
+    options: {},
+    transformOptions: TransformOptions,
+    onProgress?: ?(finishedModules: number, totalModules: number) => mixed,
+    getModuleId: mixed,
+  ): Promise<ResolutionResponse> {
     const {platform, recursive} = getDependenciesValidateOpts(options);
     return this._depGraph.getDependencies({
       entryPath,
@@ -148,7 +169,7 @@ class Resolver {
     });
   }
 
-  getModuleSystemDependencies(options) {
+  getModuleSystemDependencies(options: {}): Array<Module> {
     const opts = getDependenciesValidateOpts(options);
 
     const prelude = opts.dev
@@ -167,7 +188,7 @@ class Resolver {
     }));
   }
 
-  _getPolyfillDependencies() {
+  _getPolyfillDependencies(): Array<Module> {
     const polyfillModuleNames = defaults.polyfills.concat(this._polyfillModuleNames);
 
     return polyfillModuleNames.map(
@@ -179,7 +200,12 @@ class Resolver {
     );
   }
 
-  resolveRequires(resolutionResponse, module, code, dependencyOffsets = []) {
+  resolveRequires(
+    resolutionResponse: ResolutionResponse,
+    module: Module,
+    code: string,
+    dependencyOffsets: Array<number> = [],
+  ): string {
     const resolvedDeps = Object.create(null);
 
     // here, we build a map of all require strings (relative and absolute)
@@ -187,6 +213,7 @@ class Resolver {
     resolutionResponse.getResolvedDependencyPairs(module)
       .forEach(([depName, depModule]) => {
         if (depModule) {
+          /* $FlowFixMe: `getModuleId` is monkey-patched so may not exist */
           resolvedDeps[depName] = resolutionResponse.getModuleId(depModule);
         }
       });
@@ -204,7 +231,7 @@ class Resolver {
         ? `${JSON.stringify(resolvedDeps[depName])} /* ${depName} */`
         : codeMatch;
 
-    code = dependencyOffsets.reduceRight((codeBits, offset) => {
+    const codeParts = dependencyOffsets.reduceRight((codeBits, offset) => {
       const first = codeBits.shift();
       codeBits.unshift(
         first.slice(0, offset),
@@ -213,7 +240,7 @@ class Resolver {
       return codeBits;
     }, [code]);
 
-    return code.join('');
+    return codeParts.join('');
   }
 
   wrapModule({
@@ -225,6 +252,17 @@ class Resolver {
     meta = {},
     dev = true,
     minify = false,
+  }: {
+    resolutionResponse: ResolutionResponse,
+    module: Module,
+    name: string,
+    map: SourceMap,
+    code: string,
+    meta?: {
+      dependencyOffsets?: Array<number>,
+    },
+    dev?: boolean,
+    minify?: boolean,
   }) {
     if (module.isJSON()) {
       code = `module.exports = ${code}`;
@@ -233,6 +271,7 @@ class Resolver {
     if (module.isPolyfill()) {
       code = definePolyfillCode(code);
     } else {
+      /* $FlowFixMe: `getModuleId` is monkey-patched so may not exist */
       const moduleId = resolutionResponse.getModuleId(module);
       code = this.resolveRequires(
         resolutionResponse,
@@ -243,17 +282,18 @@ class Resolver {
       code = defineModuleCode(moduleId, code, name, dev);
     }
 
-
     return minify
       ? this._minifyCode(module.path, code, map)
       : Promise.resolve({code, map});
   }
 
-  minifyModule({path, code, map}) {
+  minifyModule(
+    {path, code, map}: {path: string, code: string, map: SourceMap},
+  ): Promise<{code: string, map: SourceMap}> {
     return this._minifyCode(path, code, map);
   }
 
-  getDependencyGraph() {
+  getDependencyGraph(): DependencyGraph {
     return this._depGraph;
   }
 }
diff --git a/packager/react-packager/src/lib/TransformCache.js b/packager/react-packager/src/lib/TransformCache.js
index 69f48584c..b6638f75b 100644
--- a/packager/react-packager/src/lib/TransformCache.js
+++ b/packager/react-packager/src/lib/TransformCache.js
@@ -29,6 +29,7 @@ const CACHE_NAME = 'react-native-packager-cache';
 
 type CacheFilePaths = {transformedCode: string, metadata: string};
 import type {Options as TransformOptions} from '../JSTransformer/worker/worker';
+import type {SourceMap} from './SourceMap';
 
 /**
  * If packager is running for two different directories, we don't want the
@@ -79,7 +80,7 @@ export type CachedResult = {
   code: string,
   dependencies: Array<string>,
   dependencyOffsets: Array<number>,
-  map?: ?{},
+  map?: ?SourceMap,
 };
 
 /**
@@ -227,7 +228,7 @@ function readMetadataFileSync(
   cachedSourceHash: number,
   dependencies: Array<string>,
   dependencyOffsets: Array<number>,
-  sourceMap: ?{},
+  sourceMap: ?SourceMap,
 } {
   const metadataStr = fs.readFileSync(metadataFilePath, 'utf8');
   let metadata;
diff --git a/packager/react-packager/src/node-haste/DependencyGraph/ResolutionRequest.js b/packager/react-packager/src/node-haste/DependencyGraph/ResolutionRequest.js
index e3b5cdfaa..52a892935 100644
--- a/packager/react-packager/src/node-haste/DependencyGraph/ResolutionRequest.js
+++ b/packager/react-packager/src/node-haste/DependencyGraph/ResolutionRequest.js
@@ -124,7 +124,7 @@ class ResolutionRequest {
   }: {
     response: ResolutionResponse,
     transformOptions: Object,
-    onProgress: () => void,
+    onProgress?: ?(finishedModules: number, totalModules: number) => mixed,
     recursive: boolean,
   }) {
     const entry = this._moduleCache.getModule(this._entryPath);
diff --git a/packager/react-packager/src/node-haste/DependencyGraph/ResolutionResponse.js b/packager/react-packager/src/node-haste/DependencyGraph/ResolutionResponse.js
index 63ce48ef7..8ed5d91f1 100644
--- a/packager/react-packager/src/node-haste/DependencyGraph/ResolutionResponse.js
+++ b/packager/react-packager/src/node-haste/DependencyGraph/ResolutionResponse.js
@@ -13,21 +13,26 @@
 
 import Module from '../Module';
 
+import type {Options as TransformOptions} from '../../JSTransformer/worker/worker';
+
 const NO_OPTIONS = {};
 
 class ResolutionResponse {
 
-  transformOptions: {};
+  transformOptions: TransformOptions;
   dependencies: Array<Module>;
   mainModuleId: ?(number | string);
   mocks: mixed;
   numPrependedDependencies: number;
 
+  // This is monkey-patched from Resolver.
+  getModuleId: ?() => number;
+
   _mappings: {};
   _finalized: boolean;
   _mainModule: ?Module;
 
-  constructor({transformOptions}: {transformOptions: {}}) {
+  constructor({transformOptions}: {transformOptions: TransformOptions}) {
     this.transformOptions = transformOptions;
     this.dependencies = [];
     this.mainModuleId = null;
@@ -76,7 +81,7 @@ class ResolutionResponse {
     }
   }
 
-  finalize() {
+  finalize(): ResolutionResponse {
     /* $FlowFixMe: _mainModule is not initialized in the constructor. */
     return this._mainModule.getName().then(id => {
       this.mainModuleId = id;
diff --git a/packager/react-packager/src/node-haste/Module.js b/packager/react-packager/src/node-haste/Module.js
index acdb5c117..0435843f0 100644
--- a/packager/react-packager/src/node-haste/Module.js
+++ b/packager/react-packager/src/node-haste/Module.js
@@ -25,16 +25,18 @@ const jsonStableStringify = require('json-stable-stringify');
 const {join: joinPath, relative: relativePath, extname} = require('path');
 
 import type {TransformedCode, Options as TransformOptions} from '../JSTransformer/worker/worker';
+import type {SourceMap} from '../lib/SourceMap';
 import type {ReadTransformProps} from '../lib/TransformCache';
 import type Cache from './Cache';
 import type DependencyGraphHelpers from './DependencyGraph/DependencyGraphHelpers';
 import type ModuleCache from './ModuleCache';
 
 type ReadResult = {
-  code?: string,
+  code: string,
   dependencies?: ?Array<string>,
   dependencyOffsets?: ?Array<number>,
-  map?: ?{},
+  map?: ?SourceMap,
+  source: string,
 };
 
 export type TransformCode = (
@@ -122,7 +124,7 @@ class Module {
     return this.read(transformOptions).then(({map}) => map);
   }
 
-  getName(): Promise<string | number> {
+  getName(): Promise<string> {
     return this._cache.get(
       this.path,
       'name',
@@ -209,9 +211,10 @@ class Module {
     id?: string,
     extern: boolean,
     result: TransformedCode,
-  ) {
+  ): ReadResult {
     if (this._options.cacheTransformResults === false) {
       const {dependencies} = result;
+      /* $FlowFixMe: this code path is dead, remove. */
       return {dependencies};
     }
     return {...result, id, source};
diff --git a/packager/react-packager/src/node-haste/index.js b/packager/react-packager/src/node-haste/index.js
index 3667077d9..4595d1557 100644
--- a/packager/react-packager/src/node-haste/index.js
+++ b/packager/react-packager/src/node-haste/index.js
@@ -38,6 +38,7 @@ const {
   print,
 } = require('../Logger');
 
+import type {Options as TransformOptions} from '../JSTransformer/worker/worker';
 import type {
   Options as ModuleOptions,
   TransformCode,
@@ -53,7 +54,7 @@ class DependencyGraph {
     extraNodeModules: Object,
     forceNodeFilesystemAPI: boolean,
     ignoreFilePath: (filePath: string) => boolean,
-    maxWorkers: number,
+    maxWorkers: ?number,
     mocksPattern: mixed,
     moduleOptions: ModuleOptions,
     platforms: Set<string>,
@@ -103,22 +104,22 @@ class DependencyGraph {
     assetDependencies: mixed,
     assetExts: Array<string>,
     cache: Cache,
-    extensions: Array<string>,
+    extensions?: ?Array<string>,
     extraNodeModules: Object,
     forceNodeFilesystemAPI?: boolean,
     ignoreFilePath: (filePath: string) => boolean,
-    maxWorkers: number,
-    mocksPattern: mixed,
+    maxWorkers?: ?number,
+    mocksPattern?: mixed,
     moduleOptions: ?ModuleOptions,
     platforms: mixed,
     preferNativePlatform: boolean,
     providesModuleNodeModules: Array<string>,
     resetCache: boolean,
     roots: Array<string>,
-    shouldThrowOnUnresolvedErrors: () => boolean,
+    shouldThrowOnUnresolvedErrors?: () => boolean,
     transformCacheKey: string,
     transformCode: TransformCode,
-    useWatchman: boolean,
+    useWatchman?: ?boolean,
     watch: boolean,
   }) {
     this._opts = {
@@ -272,8 +273,8 @@ class DependencyGraph {
   }: {
     entryPath: string,
     platform: string,
-    transformOptions: {},
-    onProgress: () => void,
+    transformOptions: TransformOptions,
+    onProgress?: ?(finishedModules: number, totalModules: number) => mixed,
     recursive: boolean,
   }) {
     return this.load().then(() => {