diff --git a/packages/react-art/package.json b/packages/react-art/package.json
index 1f9ff696504f5..abd5b813e8c13 100644
--- a/packages/react-art/package.json
+++ b/packages/react-art/package.json
@@ -19,8 +19,7 @@
   "homepage": "https://facebook.github.io/react/",
   "dependencies": {
     "fbjs": "^0.8.9",
-    "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.0"
+    "loose-envify": "^1.1.0"
   },
   "peerDependencies": {
     "react": "^16.0.0-alpha.13"
diff --git a/packages/react-dom/package.json b/packages/react-dom/package.json
index 34fe03bf7d243..f8631967f0496 100644
--- a/packages/react-dom/package.json
+++ b/packages/react-dom/package.json
@@ -15,7 +15,6 @@
   "dependencies": {
     "fbjs": "^0.8.9",
     "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.0",
     "prop-types": "^15.5.6"
   },
   "peerDependencies": {
diff --git a/packages/react-noop-renderer/package.json b/packages/react-noop-renderer/package.json
index 1c148ecc2666e..a709d3cfbf450 100644
--- a/packages/react-noop-renderer/package.json
+++ b/packages/react-noop-renderer/package.json
@@ -7,8 +7,7 @@
   "repository": "facebook/react",
   "license": "BSD-3-Clause",
   "dependencies": {
-    "fbjs": "^0.8.9",
-    "object-assign": "^4.1.0"
+    "fbjs": "^0.8.9"
   },
   "files": [
     "LICENSE",
diff --git a/packages/react-test-renderer/package.json b/packages/react-test-renderer/package.json
index 6fc32c5739798..bbb02f2e5bc7a 100644
--- a/packages/react-test-renderer/package.json
+++ b/packages/react-test-renderer/package.json
@@ -15,8 +15,7 @@
   },
   "homepage": "https://facebook.github.io/react/",
   "dependencies": {
-    "fbjs": "^0.8.9",
-    "object-assign": "^4.1.0"
+    "fbjs": "^0.8.9"
   },
   "peerDependencies": {
     "react": "^16.0.0-alpha.13"
diff --git a/packages/react/package.json b/packages/react/package.json
index ef5c5bb7cdc3b..7cbc551561159 100644
--- a/packages/react/package.json
+++ b/packages/react/package.json
@@ -24,7 +24,6 @@
   "dependencies": {
     "fbjs": "^0.8.9",
     "loose-envify": "^1.1.0",
-    "object-assign": "^4.1.0",
     "prop-types": "^15.5.6"
   },
   "browserify": {
diff --git a/scripts/babel/transform-object-assign-require.js b/scripts/babel/transform-object-assign-require.js
deleted file mode 100644
index d11fba2466361..0000000000000
--- a/scripts/babel/transform-object-assign-require.js
+++ /dev/null
@@ -1,51 +0,0 @@
-/**
- * Copyright 2013-present, Facebook, Inc.
- * All rights reserved.
- *
- * 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.
- */
-
-'use strict';
-
-module.exports = function autoImporter(babel) {
-  const t = babel.types;
-
-  function getAssignIdent(path, file, state) {
-    if (!state.id) {
-      state.id = path.scope.generateUidIdentifier('assign');
-      path.scope.getProgramParent().push({
-        id: state.id,
-        init: t.callExpression(t.identifier('require'), [
-          t.stringLiteral('object-assign'),
-        ]),
-      });
-    }
-    return state.id;
-  }
-
-  return {
-    pre: function() {
-      // map from module to generated identifier
-      this.id = null;
-    },
-
-    visitor: {
-      CallExpression: function(path, file) {
-        if (path.get('callee').matchesPattern('Object.assign')) {
-          // generate identifier and require if it hasn't been already
-          var id = getAssignIdent(path, file, this);
-          path.node.callee = id;
-        }
-      },
-
-      MemberExpression: function(path, file) {
-        if (path.matchesPattern('Object.assign')) {
-          var id = getAssignIdent(path, file, this);
-          path.replaceWith(id);
-        }
-      },
-    },
-  };
-};
diff --git a/scripts/jest/preprocessor.js b/scripts/jest/preprocessor.js
index 5f661d1aabbf4..76844cabb5b4a 100644
--- a/scripts/jest/preprocessor.js
+++ b/scripts/jest/preprocessor.js
@@ -43,9 +43,7 @@ var babelOptions = {
     [
       babelPluginModules,
       {
-        map: Object.assign({}, moduleMap, {
-          'object-assign': 'object-assign',
-        }),
+        map: moduleMap,
       },
     ],
     // Keep stacks detailed in tests.
diff --git a/scripts/rollup/build.js b/scripts/rollup/build.js
index 33662d9caaf92..fcd026c9e7bac 100644
--- a/scripts/rollup/build.js
+++ b/scripts/rollup/build.js
@@ -9,7 +9,6 @@ const replace = require('rollup-plugin-replace');
 const chalk = require('chalk');
 const escapeStringRegexp = require('escape-string-regexp');
 const join = require('path').join;
-const resolve = require('path').resolve;
 const fs = require('fs');
 const rimraf = require('rimraf');
 const argv = require('minimist')(process.argv.slice(2));
@@ -124,8 +123,6 @@ function updateBabelConfig(babelOpts, bundleType) {
     case NODE_PROD:
       return Object.assign({}, babelOpts, {
         plugins: babelOpts.plugins.concat([
-          // Use object-assign polyfill in open source
-          resolve('./scripts/babel/transform-object-assign-require'),
           // Replace __DEV__ with process.env.NODE_ENV and minify invariant messages
           require('../error-codes/dev-expression-with-codes'),
         ]),
diff --git a/scripts/rollup/modules.js b/scripts/rollup/modules.js
index 5907a23757d7c..4ebd963d84bde 100644
--- a/scripts/rollup/modules.js
+++ b/scripts/rollup/modules.js
@@ -88,14 +88,10 @@ function createModuleMap(paths, extractErrors, bundleType) {
 }
 
 function getNodeModules(bundleType) {
-  // rather than adding the rollup node resolve plugin,
-  // we can instead deal with the only node module that is used
-  // for UMD bundles - object-assign
   switch (bundleType) {
     case UMD_DEV:
     case UMD_PROD:
       return {
-        'object-assign': resolve('./node_modules/object-assign/index.js'),
         // include the ART package modules directly by aliasing them from node_modules
         'art/modes/current': resolve('./node_modules/art/modes/current.js'),
         'art/modes/fast-noSideEffects': resolve(
@@ -156,8 +152,6 @@ function getExternalModules(externals, bundleType, isRenderer) {
     case RN_DEV:
     case RN_PROD:
       fbjsModules.forEach(module => externalModules.push(module));
-      externalModules.push('object-assign');
-
       if (isRenderer) {
         externalModules.push('react');
       }
diff --git a/scripts/rollup/results.json b/scripts/rollup/results.json
index d419dbe5d1612..954294bbcd8ad 100644
--- a/scripts/rollup/results.json
+++ b/scripts/rollup/results.json
@@ -1,20 +1,20 @@
 {
   "bundleSizes": {
     "react.development.js (UMD_DEV)": {
-      "size": 65928,
-      "gzip": 16792
+      "size": 63860,
+      "gzip": 16063
     },
     "react.production.min.js (UMD_PROD)": {
-      "size": 6738,
-      "gzip": 2759
+      "size": 5854,
+      "gzip": 2398
     },
     "react.development.js (NODE_DEV)": {
-      "size": 56228,
-      "gzip": 14438
+      "size": 56177,
+      "gzip": 14420
     },
     "react.production.min.js (NODE_PROD)": {
-      "size": 5598,
-      "gzip": 2334
+      "size": 5605,
+      "gzip": 2327
     },
     "React-dev.js (FB_DEV)": {
       "size": 53485,
@@ -25,20 +25,20 @@
       "gzip": 6705
     },
     "react-dom.development.js (UMD_DEV)": {
-      "size": 630876,
-      "gzip": 143999
+      "size": 628906,
+      "gzip": 143288
     },
     "react-dom.production.min.js (UMD_PROD)": {
-      "size": 127001,
-      "gzip": 40233
+      "size": 126236,
+      "gzip": 39919
     },
     "react-dom.development.js (NODE_DEV)": {
-      "size": 590270,
-      "gzip": 134359
+      "size": 590326,
+      "gzip": 134354
     },
     "react-dom.production.min.js (NODE_PROD)": {
-      "size": 123917,
-      "gzip": 39159
+      "size": 124043,
+      "gzip": 39170
     },
     "ReactDOMFiber-dev.js (FB_DEV)": {
       "size": 589473,
@@ -65,20 +65,20 @@
       "gzip": 81957
     },
     "react-dom-server.development.js (UMD_DEV)": {
-      "size": 121172,
-      "gzip": 30762
+      "size": 119150,
+      "gzip": 30045
     },
     "react-dom-server.production.min.js (UMD_PROD)": {
-      "size": 20365,
-      "gzip": 7841
+      "size": 19541,
+      "gzip": 7501
     },
     "react-dom-server.development.js (NODE_DEV)": {
-      "size": 90322,
-      "gzip": 23339
+      "size": 90286,
+      "gzip": 23330
     },
     "react-dom-server.production.min.js (NODE_PROD)": {
-      "size": 18871,
-      "gzip": 7306
+      "size": 18938,
+      "gzip": 7302
     },
     "ReactDOMServerStream-dev.js (FB_DEV)": {
       "size": 264750,
@@ -189,12 +189,12 @@
       "gzip": 13644
     },
     "react-dom-node-stream.development.js (NODE_DEV)": {
-      "size": 92016,
-      "gzip": 23840
+      "size": 91980,
+      "gzip": 23825
     },
     "react-dom-node-stream.production.min.js (NODE_PROD)": {
-      "size": 19808,
-      "gzip": 7646
+      "size": 19875,
+      "gzip": 7641
     },
     "ReactDOMNodeStream-dev.js (FB_DEV)": {
       "size": 264918,
@@ -205,20 +205,20 @@
       "gzip": 50956
     },
     "react-dom-unstable-native-dependencies.development.js (UMD_DEV)": {
-      "size": 87163,
-      "gzip": 21689
+      "size": 85091,
+      "gzip": 20954
     },
     "react-dom-unstable-native-dependencies.production.min.js (UMD_PROD)": {
-      "size": 18899,
-      "gzip": 6159
+      "size": 18013,
+      "gzip": 5783
     },
     "react-dom-unstable-native-dependencies.development.js (NODE_DEV)": {
-      "size": 80583,
-      "gzip": 19737
+      "size": 80533,
+      "gzip": 19717
     },
     "react-dom-unstable-native-dependencies.production.min.js (NODE_PROD)": {
-      "size": 17154,
-      "gzip": 5513
+      "size": 17160,
+      "gzip": 5515
     },
     "ReactDOMUnstableNativeDependencies-dev.js (FB_DEV)": {
       "size": 79722,