diff --git a/src/addons/transitions/ReactCSSTransitionGroup.js b/src/addons/transitions/ReactCSSTransitionGroup.js
index c54d9a7aeb..5b6ce5607c 100644
--- a/src/addons/transitions/ReactCSSTransitionGroup.js
+++ b/src/addons/transitions/ReactCSSTransitionGroup.js
@@ -28,8 +28,6 @@ var ReactCSSTransitionGroupChild = React.createFactory(
   require('ReactCSSTransitionGroupChild')
 );
 
-var merge = require('merge');
-
 var ReactCSSTransitionGroup = React.createClass({
   displayName: 'ReactCSSTransitionGroup',
 
@@ -63,7 +61,7 @@ var ReactCSSTransitionGroup = React.createClass({
   render: function() {
     return (
       ReactTransitionGroup(
-        merge(this.props, {childFactory: this._wrapChild})
+        Object.assign({}, this.props, {childFactory: this._wrapChild})
       )
     );
   }
diff --git a/src/addons/transitions/ReactTransitionGroup.js b/src/addons/transitions/ReactTransitionGroup.js
index 174d389676..1203abb703 100644
--- a/src/addons/transitions/ReactTransitionGroup.js
+++ b/src/addons/transitions/ReactTransitionGroup.js
@@ -23,7 +23,6 @@ var ReactTransitionChildMapping = require('ReactTransitionChildMapping');
 
 var cloneWithProps = require('cloneWithProps');
 var emptyFunction = require('emptyFunction');
-var merge = require('merge');
 
 var ReactTransitionGroup = React.createClass({
   displayName: 'ReactTransitionGroup',
@@ -159,7 +158,7 @@ var ReactTransitionGroup = React.createClass({
       // This entered again before it fully left. Add it again.
       this.performEnter(key);
     } else {
-      var newChildren = merge(this.state.children);
+      var newChildren = Object.assign({}, this.state.children);
       delete newChildren[key];
       this.setState({children: newChildren});
     }
diff --git a/src/addons/update.js b/src/addons/update.js
index 43ec8dd53f..c55f4b13dd 100644
--- a/src/addons/update.js
+++ b/src/addons/update.js
@@ -18,7 +18,6 @@
 
 "use strict";
 
-var copyProperties = require('copyProperties');
 var keyOf = require('keyOf');
 var invariant = require('invariant');
 
@@ -26,7 +25,7 @@ function shallowCopy(x) {
   if (Array.isArray(x)) {
     return x.concat();
   } else if (x && typeof x === 'object') {
-    return copyProperties(new x.constructor(), x);
+    return Object.assign(new x.constructor(), x);
   } else {
     return x;
   }
@@ -106,7 +105,7 @@ function update(value, spec) {
       COMMAND_MERGE,
       nextValue
     );
-    copyProperties(nextValue, spec[COMMAND_MERGE]);
+    Object.assign(nextValue, spec[COMMAND_MERGE]);
   }
 
   if (spec.hasOwnProperty(COMMAND_PUSH)) {
diff --git a/src/browser/ReactBrowserEventEmitter.js b/src/browser/ReactBrowserEventEmitter.js
index 677b076986..62d65347b7 100644
--- a/src/browser/ReactBrowserEventEmitter.js
+++ b/src/browser/ReactBrowserEventEmitter.js
@@ -26,7 +26,6 @@ var ReactEventEmitterMixin = require('ReactEventEmitterMixin');
 var ViewportMetrics = require('ViewportMetrics');
 
 var isEventSupported = require('isEventSupported');
-var merge = require('merge');
 
 /**
  * Summary of `ReactBrowserEventEmitter` event handling:
@@ -155,7 +154,7 @@ function getListeningForDocument(mountAt) {
  *
  * @internal
  */
-var ReactBrowserEventEmitter = merge(ReactEventEmitterMixin, {
+var ReactBrowserEventEmitter = Object.assign({}, ReactEventEmitterMixin, {
 
   /**
    * Injectable event backend
diff --git a/src/browser/ReactPutListenerQueue.js b/src/browser/ReactPutListenerQueue.js
index 0e2500e499..31256aaaaf 100644
--- a/src/browser/ReactPutListenerQueue.js
+++ b/src/browser/ReactPutListenerQueue.js
@@ -21,13 +21,11 @@
 var PooledClass = require('PooledClass');
 var ReactBrowserEventEmitter = require('ReactBrowserEventEmitter');
 
-var mixInto = require('mixInto');
-
 function ReactPutListenerQueue() {
   this.listenersToPut = [];
 }
 
-mixInto(ReactPutListenerQueue, {
+Object.assign(ReactPutListenerQueue.prototype, {
   enqueuePutListener: function(rootNodeID, propKey, propValue) {
     this.listenersToPut.push({
       rootNodeID: rootNodeID,
diff --git a/src/browser/ReactReconcileTransaction.js b/src/browser/ReactReconcileTransaction.js
index e4ac1ffa02..42c88cbca2 100644
--- a/src/browser/ReactReconcileTransaction.js
+++ b/src/browser/ReactReconcileTransaction.js
@@ -26,8 +26,6 @@ var ReactInputSelection = require('ReactInputSelection');
 var ReactPutListenerQueue = require('ReactPutListenerQueue');
 var Transaction = require('Transaction');
 
-var mixInto = require('mixInto');
-
 /**
  * Ensures that, when possible, the selection range (currently selected text
  * input) is not disturbed by performing the transaction.
@@ -174,8 +172,7 @@ var Mixin = {
 };
 
 
-mixInto(ReactReconcileTransaction, Transaction.Mixin);
-mixInto(ReactReconcileTransaction, Mixin);
+Object.assign(ReactReconcileTransaction.prototype, Transaction.Mixin, Mixin);
 
 PooledClass.addPoolingTo(ReactReconcileTransaction);
 
diff --git a/src/browser/ReactTextComponent.js b/src/browser/ReactTextComponent.js
index 25cdd6e1bf..aa2819fff6 100644
--- a/src/browser/ReactTextComponent.js
+++ b/src/browser/ReactTextComponent.js
@@ -25,7 +25,6 @@ var ReactComponent = require('ReactComponent');
 var ReactElement = require('ReactElement');
 
 var escapeTextForBrowser = require('escapeTextForBrowser');
-var mixInto = require('mixInto');
 
 /**
  * Text nodes violate a couple assumptions that React makes about components:
@@ -46,8 +45,7 @@ var ReactTextComponent = function(props) {
   // This constructor and it's argument is currently used by mocks.
 };
 
-mixInto(ReactTextComponent, ReactComponent.Mixin);
-mixInto(ReactTextComponent, {
+Object.assign(ReactTextComponent.prototype, ReactComponent.Mixin, {
 
   /**
    * Creates the markup for this text node. This node is not intended to have
diff --git a/src/browser/server/ReactServerRenderingTransaction.js b/src/browser/server/ReactServerRenderingTransaction.js
index 2251f82f96..7b7d8f86b6 100644
--- a/src/browser/server/ReactServerRenderingTransaction.js
+++ b/src/browser/server/ReactServerRenderingTransaction.js
@@ -25,7 +25,6 @@ var ReactPutListenerQueue = require('ReactPutListenerQueue');
 var Transaction = require('Transaction');
 
 var emptyFunction = require('emptyFunction');
-var mixInto = require('mixInto');
 
 /**
  * Provides a `CallbackQueue` queue for collecting `onDOMReady` callbacks
@@ -107,8 +106,11 @@ var Mixin = {
 };
 
 
-mixInto(ReactServerRenderingTransaction, Transaction.Mixin);
-mixInto(ReactServerRenderingTransaction, Mixin);
+Object.assign(
+  ReactServerRenderingTransaction.prototype,
+  Transaction.Mixin,
+  Mixin
+);
 
 PooledClass.addPoolingTo(ReactServerRenderingTransaction);
 
diff --git a/src/browser/syntheticEvents/SyntheticEvent.js b/src/browser/syntheticEvents/SyntheticEvent.js
index f6012d59cf..ae3fb6c54b 100644
--- a/src/browser/syntheticEvents/SyntheticEvent.js
+++ b/src/browser/syntheticEvents/SyntheticEvent.js
@@ -23,8 +23,6 @@ var PooledClass = require('PooledClass');
 
 var emptyFunction = require('emptyFunction');
 var getEventTarget = require('getEventTarget');
-var merge = require('merge');
-var mergeInto = require('mergeInto');
 
 /**
  * @interface Event
@@ -91,7 +89,7 @@ function SyntheticEvent(dispatchConfig, dispatchMarker, nativeEvent) {
   this.isPropagationStopped = emptyFunction.thatReturnsFalse;
 }
 
-mergeInto(SyntheticEvent.prototype, {
+Object.assign(SyntheticEvent.prototype, {
 
   preventDefault: function() {
     this.defaultPrevented = true;
@@ -149,11 +147,11 @@ SyntheticEvent.augmentClass = function(Class, Interface) {
   var Super = this;
 
   var prototype = Object.create(Super.prototype);
-  mergeInto(prototype, Class.prototype);
+  Object.assign(prototype, Class.prototype);
   Class.prototype = prototype;
   Class.prototype.constructor = Class;
 
-  Class.Interface = merge(Super.Interface, Interface);
+  Class.Interface = Object.assign({}, Super.Interface, Interface);
   Class.augmentClass = Super.augmentClass;
 
   PooledClass.addPoolingTo(Class, PooledClass.threeArgumentPooler);
diff --git a/src/browser/ui/ReactDOMComponent.js b/src/browser/ui/ReactDOMComponent.js
index cbbe776d3d..a7536c71c7 100644
--- a/src/browser/ui/ReactDOMComponent.js
+++ b/src/browser/ui/ReactDOMComponent.js
@@ -33,8 +33,6 @@ var escapeTextForBrowser = require('escapeTextForBrowser');
 var invariant = require('invariant');
 var isEventSupported = require('isEventSupported');
 var keyOf = require('keyOf');
-var merge = require('merge');
-var mixInto = require('mixInto');
 var monitorCodeUse = require('monitorCodeUse');
 
 var deleteListener = ReactBrowserEventEmitter.deleteListener;
@@ -207,7 +205,7 @@ ReactDOMComponent.Mixin = {
       } else {
         if (propKey === STYLE) {
           if (propValue) {
-            propValue = props.style = merge(props.style);
+            propValue = props.style = Object.assign({}, props.style);
           }
           propValue = CSSPropertyOperations.createMarkupForStyles(propValue);
         }
@@ -356,7 +354,7 @@ ReactDOMComponent.Mixin = {
       }
       if (propKey === STYLE) {
         if (nextProp) {
-          nextProp = nextProps.style = merge(nextProp);
+          nextProp = nextProps.style = Object.assign({}, nextProp);
         }
         if (lastProp) {
           // Unset styles on `lastProp` but not on `nextProp`.
@@ -465,9 +463,12 @@ ReactDOMComponent.Mixin = {
 
 };
 
-mixInto(ReactDOMComponent, ReactComponent.Mixin);
-mixInto(ReactDOMComponent, ReactDOMComponent.Mixin);
-mixInto(ReactDOMComponent, ReactMultiChild.Mixin);
-mixInto(ReactDOMComponent, ReactBrowserComponentMixin);
+Object.assign(
+  ReactDOMComponent.prototype,
+  ReactComponent.Mixin,
+  ReactDOMComponent.Mixin,
+  ReactMultiChild.Mixin,
+  ReactBrowserComponentMixin
+);
 
 module.exports = ReactDOMComponent;
diff --git a/src/browser/ui/ReactEventListener.js b/src/browser/ui/ReactEventListener.js
index 5dc6683bb7..c032b5483e 100644
--- a/src/browser/ui/ReactEventListener.js
+++ b/src/browser/ui/ReactEventListener.js
@@ -28,7 +28,6 @@ var ReactUpdates = require('ReactUpdates');
 
 var getEventTarget = require('getEventTarget');
 var getUnboundedScrollPosition = require('getUnboundedScrollPosition');
-var mixInto = require('mixInto');
 
 /**
  * Finds the parent React component of `node`.
@@ -54,7 +53,7 @@ function TopLevelCallbackBookKeeping(topLevelType, nativeEvent) {
   this.nativeEvent = nativeEvent;
   this.ancestors = [];
 }
-mixInto(TopLevelCallbackBookKeeping, {
+Object.assign(TopLevelCallbackBookKeeping.prototype, {
   destructor: function() {
     this.topLevelType = null;
     this.nativeEvent = null;
diff --git a/src/browser/ui/__tests__/ReactDOMComponent-test.js b/src/browser/ui/__tests__/ReactDOMComponent-test.js
index 3da6798f7a..7e5274c9f7 100644
--- a/src/browser/ui/__tests__/ReactDOMComponent-test.js
+++ b/src/browser/ui/__tests__/ReactDOMComponent-test.js
@@ -224,7 +224,6 @@ describe('ReactDOMComponent', function() {
       var ReactDefaultInjection = require('ReactDefaultInjection');
       ReactDefaultInjection.inject();
 
-      var mixInto = require('mixInto');
       var ReactDOMComponent = require('ReactDOMComponent');
       var ReactReconcileTransaction = require('ReactReconcileTransaction');
 
@@ -232,7 +231,7 @@ describe('ReactDOMComponent', function() {
         this.props = initialProps || {};
         this._rootNodeID = 'test';
       };
-      mixInto(NodeStub, ReactDOMComponent.Mixin);
+      Object.assign(NodeStub.prototype, ReactDOMComponent.Mixin);
 
       genMarkup = function(props) {
         var transaction = new ReactReconcileTransaction();
@@ -275,7 +274,6 @@ describe('ReactDOMComponent', function() {
     beforeEach(function() {
       require('mock-modules').dumpCache();
 
-      var mixInto = require('mixInto');
       var ReactDOMComponent = require('ReactDOMComponent');
       var ReactReconcileTransaction = require('ReactReconcileTransaction');
 
@@ -283,7 +281,7 @@ describe('ReactDOMComponent', function() {
         this.props = initialProps || {};
         this._rootNodeID = 'test';
       };
-      mixInto(NodeStub, ReactDOMComponent.Mixin);
+      Object.assign(NodeStub.prototype, ReactDOMComponent.Mixin);
 
       genMarkup = function(props) {
         var transaction = new ReactReconcileTransaction();
@@ -312,7 +310,6 @@ describe('ReactDOMComponent', function() {
     beforeEach(function() {
       require('mock-modules').dumpCache();
 
-      var mixInto = require('mixInto');
       var ReactComponent = require('ReactComponent');
       var ReactMultiChild = require('ReactMultiChild');
       var ReactDOMComponent = require('ReactDOMComponent');
@@ -321,9 +318,9 @@ describe('ReactDOMComponent', function() {
       var StubNativeComponent = function(element) {
         ReactComponent.Mixin.construct.call(this, element);
       };
-      mixInto(StubNativeComponent, ReactComponent.Mixin);
-      mixInto(StubNativeComponent, ReactDOMComponent.Mixin);
-      mixInto(StubNativeComponent, ReactMultiChild.Mixin);
+      Object.assign(StubNativeComponent.prototype, ReactComponent.Mixin);
+      Object.assign(StubNativeComponent.prototype, ReactDOMComponent.Mixin);
+      Object.assign(StubNativeComponent.prototype, ReactMultiChild.Mixin);
 
       mountComponent = function(props) {
         var transaction = new ReactReconcileTransaction();
diff --git a/src/browser/ui/dom/components/ReactDOMInput.js b/src/browser/ui/dom/components/ReactDOMInput.js
index a653d375d6..a6fbc5c530 100644
--- a/src/browser/ui/dom/components/ReactDOMInput.js
+++ b/src/browser/ui/dom/components/ReactDOMInput.js
@@ -29,7 +29,6 @@ var ReactMount = require('ReactMount');
 var ReactUpdates = require('ReactUpdates');
 
 var invariant = require('invariant');
-var merge = require('merge');
 
 // Store a reference to the <input> `ReactDOMComponent`. TODO: use string
 var input = ReactElement.createFactory(ReactDOM.input.type);
@@ -74,7 +73,7 @@ var ReactDOMInput = ReactCompositeComponent.createClass({
 
   render: function() {
     // Clone `this.props` so we don't mutate the input.
-    var props = merge(this.props);
+    var props = Object.assign({}, this.props);
 
     props.defaultChecked = null;
     props.defaultValue = null;
diff --git a/src/browser/ui/dom/components/ReactDOMSelect.js b/src/browser/ui/dom/components/ReactDOMSelect.js
index dfd5d8d665..b385b2ba59 100644
--- a/src/browser/ui/dom/components/ReactDOMSelect.js
+++ b/src/browser/ui/dom/components/ReactDOMSelect.js
@@ -26,8 +26,6 @@ var ReactElement = require('ReactElement');
 var ReactDOM = require('ReactDOM');
 var ReactUpdates = require('ReactUpdates');
 
-var merge = require('merge');
-
 // Store a reference to the <select> `ReactDOMComponent`. TODO: use string
 var select = ReactElement.createFactory(ReactDOM.select.type);
 
@@ -138,7 +136,7 @@ var ReactDOMSelect = ReactCompositeComponent.createClass({
 
   render: function() {
     // Clone `this.props` so we don't mutate the input.
-    var props = merge(this.props);
+    var props = Object.assign({}, this.props);
 
     props.onChange = this._handleChange;
     props.value = null;
diff --git a/src/browser/ui/dom/components/ReactDOMTextarea.js b/src/browser/ui/dom/components/ReactDOMTextarea.js
index 9fab8e2b89..7fa5bd9fc3 100644
--- a/src/browser/ui/dom/components/ReactDOMTextarea.js
+++ b/src/browser/ui/dom/components/ReactDOMTextarea.js
@@ -28,7 +28,6 @@ var ReactDOM = require('ReactDOM');
 var ReactUpdates = require('ReactUpdates');
 
 var invariant = require('invariant');
-var merge = require('merge');
 
 var warning = require('warning');
 
@@ -103,7 +102,7 @@ var ReactDOMTextarea = ReactCompositeComponent.createClass({
 
   render: function() {
     // Clone `this.props` so we don't mutate the input.
-    var props = merge(this.props);
+    var props = Object.assign({}, this.props);
 
     invariant(
       props.dangerouslySetInnerHTML == null,
diff --git a/src/core/ReactComponent.js b/src/core/ReactComponent.js
index 139a67e72d..236cc3a71a 100644
--- a/src/core/ReactComponent.js
+++ b/src/core/ReactComponent.js
@@ -24,7 +24,6 @@ var ReactUpdates = require('ReactUpdates');
 
 var invariant = require('invariant');
 var keyMirror = require('keyMirror');
-var merge = require('merge');
 
 /**
  * Every React component is in one of these life cycles.
@@ -151,7 +150,7 @@ var ReactComponent = {
       // element props.
       var element = this._pendingElement || this._currentElement;
       this.replaceProps(
-        merge(element.props, partialProps),
+        Object.assign({}, element.props, partialProps),
         callback
       );
     },
@@ -200,7 +199,7 @@ var ReactComponent = {
       var element = this._pendingElement || this._currentElement;
       this._pendingElement = ReactElement.cloneAndReplaceProps(
         element,
-        merge(element.props, partialProps)
+        Object.assign({}, element.props, partialProps)
       );
       ReactUpdates.enqueueUpdate(this, callback);
     },
diff --git a/src/core/ReactCompositeComponent.js b/src/core/ReactCompositeComponent.js
index 6717399fdd..851ae42f89 100644
--- a/src/core/ReactCompositeComponent.js
+++ b/src/core/ReactCompositeComponent.js
@@ -37,8 +37,6 @@ var instantiateReactComponent = require('instantiateReactComponent');
 var invariant = require('invariant');
 var keyMirror = require('keyMirror');
 var keyOf = require('keyOf');
-var merge = require('merge');
-var mixInto = require('mixInto');
 var monitorCodeUse = require('monitorCodeUse');
 var mapObject = require('mapObject');
 var shouldUpdateReactComponent = require('shouldUpdateReactComponent');
@@ -349,7 +347,8 @@ var RESERVED_SPEC_KEYS = {
       childContextTypes,
       ReactPropTypeLocations.childContext
     );
-    Constructor.childContextTypes = merge(
+    Constructor.childContextTypes = Object.assign(
+      {},
       Constructor.childContextTypes,
       childContextTypes
     );
@@ -360,7 +359,11 @@ var RESERVED_SPEC_KEYS = {
       contextTypes,
       ReactPropTypeLocations.context
     );
-    Constructor.contextTypes = merge(Constructor.contextTypes, contextTypes);
+    Constructor.contextTypes = Object.assign(
+      {},
+      Constructor.contextTypes,
+      contextTypes
+    );
   },
   /**
    * Special case getDefaultProps which should move into statics but requires
@@ -382,7 +385,11 @@ var RESERVED_SPEC_KEYS = {
       propTypes,
       ReactPropTypeLocations.prop
     );
-    Constructor.propTypes = merge(Constructor.propTypes, propTypes);
+    Constructor.propTypes = Object.assign(
+      {},
+      Constructor.propTypes,
+      propTypes
+    );
   },
   statics: function(Constructor, statics) {
     mixStaticSpecIntoComponent(Constructor, statics);
@@ -462,7 +469,7 @@ function validateLifeCycleOnReplaceState(instance) {
 }
 
 /**
- * Custom version of `mixInto` which handles policy validation and reserved
+ * Mixin helper which handles policy validation and reserved
  * specification keys when building `ReactCompositeComponent` classses.
  */
 function mixSpecIntoComponent(Constructor, spec) {
@@ -866,7 +873,7 @@ var ReactCompositeComponentMixin = {
     }
     // Merge with `_pendingState` if it exists, otherwise with existing state.
     this.replaceState(
-      merge(this._pendingState || this.state, partialState),
+      Object.assign({}, this._pendingState || this.state, partialState),
       callback
     );
   },
@@ -954,7 +961,7 @@ var ReactCompositeComponentMixin = {
           name
         );
       }
-      return merge(currentContext, childContext);
+      return Object.assign({}, currentContext, childContext);
     }
     return currentContext;
   },
@@ -1332,10 +1339,13 @@ var ReactCompositeComponentMixin = {
 };
 
 var ReactCompositeComponentBase = function() {};
-mixInto(ReactCompositeComponentBase, ReactComponent.Mixin);
-mixInto(ReactCompositeComponentBase, ReactOwner.Mixin);
-mixInto(ReactCompositeComponentBase, ReactPropTransferer.Mixin);
-mixInto(ReactCompositeComponentBase, ReactCompositeComponentMixin);
+Object.assign(
+  ReactCompositeComponentBase.prototype,
+  ReactComponent.Mixin,
+  ReactOwner.Mixin,
+  ReactPropTransferer.Mixin,
+  ReactCompositeComponentMixin
+);
 
 /**
  * Module for creating composite components.
diff --git a/src/core/ReactContext.js b/src/core/ReactContext.js
index 18ce40fe3b..f7f268c53a 100644
--- a/src/core/ReactContext.js
+++ b/src/core/ReactContext.js
@@ -18,8 +18,6 @@
 
 "use strict";
 
-var merge = require('merge');
-
 /**
  * Keeps track of the current context.
  *
@@ -53,7 +51,7 @@ var ReactContext = {
   withContext: function(newContext, scopedCallback) {
     var result;
     var previousContext = ReactContext.current;
-    ReactContext.current = merge(previousContext, newContext);
+    ReactContext.current = Object.assign({}, previousContext, newContext);
     try {
       result = scopedCallback();
     } finally {
diff --git a/src/core/ReactDefaultBatchingStrategy.js b/src/core/ReactDefaultBatchingStrategy.js
index f88e9e7732..790b57f883 100644
--- a/src/core/ReactDefaultBatchingStrategy.js
+++ b/src/core/ReactDefaultBatchingStrategy.js
@@ -22,7 +22,6 @@ var ReactUpdates = require('ReactUpdates');
 var Transaction = require('Transaction');
 
 var emptyFunction = require('emptyFunction');
-var mixInto = require('mixInto');
 
 var RESET_BATCHED_UPDATES = {
   initialize: emptyFunction,
@@ -42,12 +41,15 @@ function ReactDefaultBatchingStrategyTransaction() {
   this.reinitializeTransaction();
 }
 
-mixInto(ReactDefaultBatchingStrategyTransaction, Transaction.Mixin);
-mixInto(ReactDefaultBatchingStrategyTransaction, {
-  getTransactionWrappers: function() {
-    return TRANSACTION_WRAPPERS;
+Object.assign(
+  ReactDefaultBatchingStrategyTransaction.prototype,
+  Transaction.Mixin,
+  {
+    getTransactionWrappers: function() {
+      return TRANSACTION_WRAPPERS;
+    }
   }
-});
+);
 
 var transaction = new ReactDefaultBatchingStrategyTransaction();
 
diff --git a/src/core/ReactLegacyElement.js b/src/core/ReactLegacyElement.js
index 28ef28de28..84a6bf3504 100644
--- a/src/core/ReactLegacyElement.js
+++ b/src/core/ReactLegacyElement.js
@@ -99,7 +99,7 @@ function proxyStaticMethods(target, source) {
       if (typeof value === 'function') {
         var bound = value.bind(source);
         // Copy any properties defined on the function, such as `isRequired` on
-        // a PropTypes validator. (mergeInto refuses to work on functions.)
+        // a PropTypes validator.
         for (var k in value) {
           if (value.hasOwnProperty(k)) {
             bound[k] = value[k];
diff --git a/src/core/ReactNativeComponent.js b/src/core/ReactNativeComponent.js
index 0735e2050a..d6f79a4456 100644
--- a/src/core/ReactNativeComponent.js
+++ b/src/core/ReactNativeComponent.js
@@ -19,7 +19,6 @@
 "use strict";
 
 var invariant = require('invariant');
-var mergeInto = require('mergeInto');
 
 var genericComponentClass = null;
 // This registry keeps track of wrapper classes around native tags
@@ -34,7 +33,7 @@ var ReactNativeComponentInjection = {
   // This accepts a keyed object with classes as values. Each key represents a
   // tag. That particular tag will use this class instead of the generic one.
   injectComponentClasses: function(componentClasses) {
-    mergeInto(tagToComponentClass, componentClasses);
+    Object.assign(tagToComponentClass, componentClasses);
   }
 };
 
diff --git a/src/core/ReactPropTransferer.js b/src/core/ReactPropTransferer.js
index ddba15ef49..11e7a55809 100644
--- a/src/core/ReactPropTransferer.js
+++ b/src/core/ReactPropTransferer.js
@@ -21,7 +21,6 @@
 var emptyFunction = require('emptyFunction');
 var invariant = require('invariant');
 var joinClasses = require('joinClasses');
-var merge = require('merge');
 var warning = require('warning');
 
 var didWarn = false;
@@ -47,7 +46,7 @@ var transferStrategyMerge = createTransferStrategy(function(a, b) {
   // `merge` overrides the first object's (`props[key]` above) keys using the
   // second object's (`value`) keys. An object's style's existing `propA` would
   // get overridden. Flip the order here.
-  return merge(b, a);
+  return Object.assign({}, b, a);
 });
 
 /**
@@ -113,7 +112,7 @@ var ReactPropTransferer = {
    * @return {object} a new object containing both sets of props merged.
    */
   mergeProps: function(oldProps, newProps) {
-    return transferInto(merge(oldProps), newProps);
+    return transferInto(Object.assign({}, oldProps), newProps);
   },
 
   /**
diff --git a/src/core/ReactUpdates.js b/src/core/ReactUpdates.js
index ad4a3dfdd0..8b48d15e73 100644
--- a/src/core/ReactUpdates.js
+++ b/src/core/ReactUpdates.js
@@ -25,7 +25,6 @@ var ReactPerf = require('ReactPerf');
 var Transaction = require('Transaction');
 
 var invariant = require('invariant');
-var mixInto = require('mixInto');
 var warning = require('warning');
 
 var dirtyComponents = [];
@@ -80,8 +79,9 @@ function ReactUpdatesFlushTransaction() {
     ReactUpdates.ReactReconcileTransaction.getPooled();
 }
 
-mixInto(ReactUpdatesFlushTransaction, Transaction.Mixin);
-mixInto(ReactUpdatesFlushTransaction, {
+Object.assign(
+  ReactUpdatesFlushTransaction.prototype,
+  Transaction.Mixin, {
   getTransactionWrappers: function() {
     return TRANSACTION_WRAPPERS;
   },
diff --git a/src/event/__tests__/EventPluginRegistry-test.js b/src/event/__tests__/EventPluginRegistry-test.js
index 43ed309f2e..f98420ba45 100644
--- a/src/event/__tests__/EventPluginRegistry-test.js
+++ b/src/event/__tests__/EventPluginRegistry-test.js
@@ -18,8 +18,6 @@
 
 "use strict";
 
-var merge = require('merge');
-
 describe('EventPluginRegistry', function() {
   var EventPluginRegistry;
   var createPlugin;
@@ -29,7 +27,7 @@ describe('EventPluginRegistry', function() {
     EventPluginRegistry._resetEventPlugins();
 
     createPlugin = function(properties) {
-      return merge({extractEvents: function() {}}, properties);
+      return Object.assign({extractEvents: function() {}}, properties);
     };
   });
 
diff --git a/src/test/ReactDefaultPerfAnalysis.js b/src/test/ReactDefaultPerfAnalysis.js
index 5a23916cd3..b86a17dfbe 100644
--- a/src/test/ReactDefaultPerfAnalysis.js
+++ b/src/test/ReactDefaultPerfAnalysis.js
@@ -16,8 +16,6 @@
  * @providesModule ReactDefaultPerfAnalysis
  */
 
-var merge = require('merge');
-
 // Don't try to save users less than 1.2ms (a number I made up)
 var DONT_CARE_THRESHOLD = 1.2;
 var DOM_OPERATION_TYPES = {
@@ -71,7 +69,11 @@ function getExclusiveSummary(measurements) {
 
   for (var i = 0; i < measurements.length; i++) {
     var measurement = measurements[i];
-    var allIDs = merge(measurement.exclusive, measurement.inclusive);
+    var allIDs = Object.assign(
+      {},
+      measurement.exclusive,
+      measurement.inclusive
+    );
 
     for (var id in allIDs) {
       displayName = measurement.displayNames[id].current;
@@ -119,7 +121,11 @@ function getInclusiveSummary(measurements, onlyClean) {
 
   for (var i = 0; i < measurements.length; i++) {
     var measurement = measurements[i];
-    var allIDs = merge(measurement.exclusive, measurement.inclusive);
+    var allIDs = Object.assign(
+      {},
+      measurement.exclusive,
+      measurement.inclusive
+    );
     var cleanComponents;
 
     if (onlyClean) {
@@ -174,7 +180,7 @@ function getUnchangedComponents(measurement) {
   // the amount of time it took to render the entire subtree.
   var cleanComponents = {};
   var dirtyLeafIDs = Object.keys(measurement.writes);
-  var allIDs = merge(measurement.exclusive, measurement.inclusive);
+  var allIDs = Object.assign({}, measurement.exclusive, measurement.inclusive);
 
   for (var id in allIDs) {
     var isDirty = false;
diff --git a/src/test/ReactTestUtils.js b/src/test/ReactTestUtils.js
index 1c8516545c..756af946f1 100644
--- a/src/test/ReactTestUtils.js
+++ b/src/test/ReactTestUtils.js
@@ -29,8 +29,6 @@ var ReactTextComponent = require('ReactTextComponent');
 var ReactUpdates = require('ReactUpdates');
 var SyntheticEvent = require('SyntheticEvent');
 
-var mergeInto = require('mergeInto');
-
 var topLevelTypes = EventConstants.topLevelTypes;
 
 function Event(suffix) {}
@@ -327,7 +325,7 @@ function makeSimulator(eventType) {
       ReactMount.getID(node),
       fakeNativeEvent
     );
-    mergeInto(event, eventData);
+    Object.assign(event, eventData);
     EventPropagators.accumulateTwoPhaseDispatches(event);
 
     ReactUpdates.batchedUpdates(function() {
@@ -383,7 +381,7 @@ buildSimulators();
 function makeNativeSimulator(eventType) {
   return function(domComponentOrNode, nativeEventData) {
     var fakeNativeEvent = new Event(eventType);
-    mergeInto(fakeNativeEvent, nativeEventData);
+    Object.assign(fakeNativeEvent, nativeEventData);
     if (ReactTestUtils.isDOMComponent(domComponentOrNode)) {
       ReactTestUtils.simulateNativeEventOnDOMComponent(
         eventType,
diff --git a/src/test/reactComponentExpect.js b/src/test/reactComponentExpect.js
index c040e271eb..3613238b7c 100644
--- a/src/test/reactComponentExpect.js
+++ b/src/test/reactComponentExpect.js
@@ -21,8 +21,6 @@
 
 var ReactTestUtils = require('ReactTestUtils');
 
-var mergeInto = require('mergeInto');
-
 function reactComponentExpect(instance) {
   if (instance instanceof reactComponentExpect) {
     return instance;
@@ -38,7 +36,7 @@ function reactComponentExpect(instance) {
   expect(ReactTestUtils.isElement(instance)).toBe(false);
 }
 
-mergeInto(reactComponentExpect.prototype, {
+Object.assign(reactComponentExpect.prototype, {
   // Getters -------------------------------------------------------------------
 
   /**
diff --git a/src/utils/CallbackQueue.js b/src/utils/CallbackQueue.js
index 9d989b59ec..2558d02e1c 100644
--- a/src/utils/CallbackQueue.js
+++ b/src/utils/CallbackQueue.js
@@ -21,7 +21,6 @@
 var PooledClass = require('PooledClass');
 
 var invariant = require('invariant');
-var mixInto = require('mixInto');
 
 /**
  * A specialized pseudo-event module to help keep track of components waiting to
@@ -39,7 +38,7 @@ function CallbackQueue() {
   this._contexts = null;
 }
 
-mixInto(CallbackQueue, {
+Object.assign(CallbackQueue.prototype, {
 
   /**
    * Enqueues a callback to be invoked when `notifyAll` is invoked.
diff --git a/src/utils/LegacyImmutableObject.js b/src/utils/LegacyImmutableObject.js
index e7383ae911..a3ec75f24b 100644
--- a/src/utils/LegacyImmutableObject.js
+++ b/src/utils/LegacyImmutableObject.js
@@ -21,8 +21,6 @@
 
 var invariant = require('invariant');
 var isNode = require('isNode');
-var merge = require('merge');
-var mergeInto = require('mergeInto');
 var mergeHelpers = require('mergeHelpers');
 
 var checkMergeObjectArgs = mergeHelpers.checkMergeObjectArgs;
@@ -51,7 +49,7 @@ if (__DEV__) {
    * @constructor
    */
   LegacyImmutableObject = function LegacyImmutableObject(initialProperties) {
-    mergeInto(this, initialProperties);
+    Object.assign(this, initialProperties);
     deepFreeze(this);
   };
 
@@ -100,7 +98,7 @@ if (__DEV__) {
    */
   LegacyImmutableObject.set = function(immutableObject, put) {
     assertLegacyImmutableObject(immutableObject);
-    var totalNewFields = merge(immutableObject, put);
+    var totalNewFields = Object.assign({}, immutableObject, put);
     return new LegacyImmutableObject(totalNewFields);
   };
 
@@ -112,7 +110,7 @@ if (__DEV__) {
    * @constructor
    */
   LegacyImmutableObject = function LegacyImmutableObject(initialProperties) {
-    mergeInto(this, initialProperties);
+    Object.assign(this, initialProperties);
   };
 
   /**
@@ -126,7 +124,7 @@ if (__DEV__) {
   LegacyImmutableObject.set = function(immutableObject, put) {
     assertLegacyImmutableObject(immutableObject);
     var newMap = new LegacyImmutableObject(immutableObject);
-    mergeInto(newMap, put);
+    Object.assign(newMap, put);
     return newMap;
   };
 }
diff --git a/src/utils/OrderedMap.js b/src/utils/OrderedMap.js
index 22af8f2aaf..d0b769642d 100644
--- a/src/utils/OrderedMap.js
+++ b/src/utils/OrderedMap.js
@@ -19,7 +19,6 @@
 "use strict";
 
 var invariant = require('invariant');
-var mixInto = require('mixInto');
 
 var PREFIX = 'key:';
 
@@ -483,7 +482,7 @@ var OrderedMapMethods = {
   }
 };
 
-mixInto(OrderedMapImpl, OrderedMapMethods);
+Object.assign(OrderedMapImpl.prototype, OrderedMapMethods);
 
 var OrderedMap = {
   from: function(orderedMap) {
diff --git a/src/utils/__tests__/Transaction-test.js b/src/utils/__tests__/Transaction-test.js
index 39115cd242..df8263f4d4 100644
--- a/src/utils/__tests__/Transaction-test.js
+++ b/src/utils/__tests__/Transaction-test.js
@@ -19,14 +19,12 @@
 "use strict";
 
 var Transaction;
-var mixInto;
 
 var INIT_ERRORED = 'initErrored';     // Just a dummy value to check for.
 describe('Transaction', function() {
   beforeEach(function() {
     require('mock-modules').dumpCache();
     Transaction = require('Transaction');
-    mixInto = require('mixInto');
   });
 
   /**
@@ -53,7 +51,7 @@ describe('Transaction', function() {
       this.secondCloseParam = INIT_ERRORED;  // WILL be set to something else
       this.lastCloseParam = INIT_ERRORED;    // WON'T be set to something else
     };
-    mixInto(TestTransaction, Transaction.Mixin);
+    Object.assign(TestTransaction.prototype, Transaction.Mixin);
     TestTransaction.prototype.getTransactionWrappers = function() {
       return [
         {
@@ -102,7 +100,7 @@ describe('Transaction', function() {
       this.secondCloseParam = INIT_ERRORED;  // WILL be set to something else
       this.lastCloseParam = INIT_ERRORED;    // WILL be set to something else
     };
-    mixInto(TestTransaction, Transaction.Mixin);
+    Object.assign(TestTransaction.prototype, Transaction.Mixin);
     TestTransaction.prototype.getTransactionWrappers = function() {
       return [
         {
@@ -163,7 +161,7 @@ describe('Transaction', function() {
       this.secondCloseParam = INIT_ERRORED;  // WILL be set to something else
       this.lastCloseParam = INIT_ERRORED;    // WILL be set to something else
     };
-    mixInto(TestTransaction, Transaction.Mixin);
+    Object.assign(TestTransaction.prototype, Transaction.Mixin);
     // Now, none of the close/inits throw, but the operation we wrap will throw.
     TestTransaction.prototype.getTransactionWrappers = function() {
       return [
@@ -227,7 +225,7 @@ describe('Transaction', function() {
     var TestTransaction = function() {
       this.reinitializeTransaction();
     };
-    mixInto(TestTransaction, Transaction.Mixin);
+    Object.assign(TestTransaction.prototype, Transaction.Mixin);
     var exceptionMsg = 'This exception should throw.';
     TestTransaction.prototype.getTransactionWrappers = function() {
       return [
@@ -256,7 +254,7 @@ describe('Transaction', function() {
       this.reinitializeTransaction();
       this.firstCloseParam = INIT_ERRORED; // WILL be set to something else
     };
-    mixInto(TestTransaction, Transaction.Mixin);
+    Object.assign(TestTransaction.prototype, Transaction.Mixin);
     TestTransaction.prototype.getTransactionWrappers = function() {
       return [
         {
@@ -284,7 +282,7 @@ describe('Transaction', function() {
     var NestedTransaction = function() {
       this.reinitializeTransaction();
     };
-    mixInto(NestedTransaction, Transaction.Mixin);
+    Object.assign(NestedTransaction.prototype, Transaction.Mixin);
     NestedTransaction.prototype.getTransactionWrappers = function() {
       return [{
         initialize: function() {
diff --git a/src/utils/mixInto.js b/src/utils/mixInto.js
deleted file mode 100644
index b582d1ed1c..0000000000
--- a/src/utils/mixInto.js
+++ /dev/null
@@ -1,34 +0,0 @@
-/**
- * Copyright 2013-2014 Facebook, Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- *
- * @providesModule mixInto
- */
-
-"use strict";
-
-/**
- * Simply copies properties to the prototype.
- */
-var mixInto = function(constructor, methodBag) {
-  var methodName;
-  for (methodName in methodBag) {
-    if (!methodBag.hasOwnProperty(methodName)) {
-      continue;
-    }
-    constructor.prototype[methodName] = methodBag[methodName];
-  }
-};
-
-module.exports = mixInto;
diff --git a/src/vendor/core/emptyFunction.js b/src/vendor/core/emptyFunction.js
index c9d89f2215..c06b760dae 100644
--- a/src/vendor/core/emptyFunction.js
+++ b/src/vendor/core/emptyFunction.js
@@ -16,8 +16,6 @@
  * @providesModule emptyFunction
  */
 
-var copyProperties = require('copyProperties');
-
 function makeEmptyFunction(arg) {
   return function() {
     return arg;
@@ -31,7 +29,7 @@ function makeEmptyFunction(arg) {
  */
 function emptyFunction() {}
 
-copyProperties(emptyFunction, {
+Object.assign(emptyFunction, {
   thatReturns: makeEmptyFunction,
   thatReturnsFalse: makeEmptyFunction(false),
   thatReturnsTrue: makeEmptyFunction(true),
diff --git a/src/vendor/immutable/Immutable.js b/src/vendor/immutable/Immutable.js
index 7c7559a6b5..fcd1f287c9 100644
--- a/src/vendor/immutable/Immutable.js
+++ b/src/vendor/immutable/Immutable.js
@@ -19,7 +19,6 @@
 var invariant = require('invariant');
 var isNode = require('isNode');
 var keyOf = require('keyOf');
-var mergeInto = require('mergeInto');
 
 var SECRET_KEY = keyOf({_DONT_EVER_TYPE_THIS_SECRET_KEY: null});
 
@@ -67,7 +66,7 @@ class Immutable {
   static mergeAllPropertiesInto(destination, propertyObjects) {
     var argLength = propertyObjects.length;
     for (var i = 0; i < argLength; i++) {
-      mergeInto(destination, propertyObjects[i]);
+      Object.assign(destination, propertyObjects[i]);
     }
   }