diff --git a/src/isomorphic/ReactDebugInstanceMap.js b/src/isomorphic/ReactDebugInstanceMap.js
new file mode 100644
index 0000000000000..50dddf4ad0e82
--- /dev/null
+++ b/src/isomorphic/ReactDebugInstanceMap.js
@@ -0,0 +1,124 @@
+/**
+ * Copyright 2016-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.
+ *
+ * @providesModule ReactDebugInstanceMap
+ */
+
+'use strict';
+
+var warning = require('warning');
+
+function checkValidInstance(internalInstance) {
+  if (!internalInstance) {
+    warning(
+      false,
+      'There is an internal error in the React developer tools integration. ' +
+      'Instead of an internal instance, received %s. ' +
+      'Please report this as a bug in React.',
+      internalInstance
+    );
+    return false;
+  }
+  var isValid = typeof internalInstance.mountComponent === 'function';
+  warning(
+    isValid,
+    'There is an internal error in the React developer tools integration. ' +
+    'Instead of an internal instance, received an object with the following ' +
+    'keys: %s. Please report this as a bug in React.',
+    Object.keys(internalInstance).join(', ')
+  );
+  return isValid;
+}
+
+var idCounter = 1;
+var instancesByIDs = {};
+var instancesToIDs;
+
+function getIDForInstance(internalInstance) {
+  if (!instancesToIDs) {
+    instancesToIDs = new WeakMap();
+  }
+  if (instancesToIDs.has(internalInstance)) {
+    return instancesToIDs.get(internalInstance);
+  } else {
+    var instanceID = (idCounter++).toString();
+    instancesToIDs.set(internalInstance, instanceID);
+    return instanceID;
+  }
+}
+
+function getInstanceByID(instanceID) {
+  return instancesByIDs[instanceID] || null;
+}
+
+function isRegisteredInstance(internalInstance) {
+  var instanceID = getIDForInstance(internalInstance);
+  if (instanceID) {
+    return instancesByIDs.hasOwnProperty(instanceID);
+  } else {
+    return false;
+  }
+}
+
+function registerInstance(internalInstance) {
+  var instanceID = getIDForInstance(internalInstance);
+  if (instanceID) {
+    instancesByIDs[instanceID] = internalInstance;
+  }
+}
+
+function unregisterInstance(internalInstance) {
+  var instanceID = getIDForInstance(internalInstance);
+  if (instanceID) {
+    delete instancesByIDs[instanceID];
+  }
+}
+
+var ReactDebugInstanceMap = {
+  getIDForInstance(internalInstance) {
+    if (!checkValidInstance(internalInstance)) {
+      return null;
+    }
+    return getIDForInstance(internalInstance);
+  },
+  getInstanceByID(instanceID) {
+    return getInstanceByID(instanceID);
+  },
+  isRegisteredInstance(internalInstance) {
+    if (!checkValidInstance(internalInstance)) {
+      return false;
+    }
+    return isRegisteredInstance(internalInstance);
+  },
+  registerInstance(internalInstance) {
+    if (!checkValidInstance(internalInstance)) {
+      return;
+    }
+    warning(
+      !isRegisteredInstance(internalInstance),
+      'There is an internal error in the React developer tools integration. ' +
+      'A registered instance should not be registered again. ' +
+      'Please report this as a bug in React.'
+    );
+    registerInstance(internalInstance);
+  },
+  unregisterInstance(internalInstance) {
+    if (!checkValidInstance(internalInstance)) {
+      return;
+    }
+    warning(
+      isRegisteredInstance(internalInstance),
+      'There is an internal error in the React developer tools integration. ' +
+      'An unregistered instance should not be unregistered again. ' +
+      'Please report this as a bug in React.'
+    );
+    unregisterInstance(internalInstance);
+  },
+};
+
+module.exports = ReactDebugInstanceMap;
diff --git a/src/isomorphic/__tests__/ReactDebugInstanceMap-test.js b/src/isomorphic/__tests__/ReactDebugInstanceMap-test.js
new file mode 100644
index 0000000000000..d9a063e2c649f
--- /dev/null
+++ b/src/isomorphic/__tests__/ReactDebugInstanceMap-test.js
@@ -0,0 +1,173 @@
+/**
+ * Copyright 2016-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.
+ *
+ * @emails react-core
+ */
+
+'use strict';
+
+describe('ReactDebugInstanceMap', function() {
+  var React;
+  var ReactDebugInstanceMap;
+  var ReactDOM;
+
+  beforeEach(function() {
+    jest.resetModuleRegistry();
+    React = require('React');
+    ReactDebugInstanceMap = require('ReactDebugInstanceMap');
+    ReactDOM = require('ReactDOM');
+  });
+
+  function createStubInstance() {
+    return { mountComponent: () => {} };
+  }
+
+  it('should register and unregister instances', function() {
+    var inst1 = createStubInstance();
+    var inst2 = createStubInstance();
+
+    expect(ReactDebugInstanceMap.isRegisteredInstance(inst1)).toBe(false);
+    expect(ReactDebugInstanceMap.isRegisteredInstance(inst2)).toBe(false);
+
+    ReactDebugInstanceMap.registerInstance(inst1);
+    expect(ReactDebugInstanceMap.isRegisteredInstance(inst1)).toBe(true);
+    expect(ReactDebugInstanceMap.isRegisteredInstance(inst2)).toBe(false);
+
+    ReactDebugInstanceMap.registerInstance(inst2);
+    expect(ReactDebugInstanceMap.isRegisteredInstance(inst1)).toBe(true);
+    expect(ReactDebugInstanceMap.isRegisteredInstance(inst2)).toBe(true);
+
+    ReactDebugInstanceMap.unregisterInstance(inst2);
+    expect(ReactDebugInstanceMap.isRegisteredInstance(inst1)).toBe(true);
+    expect(ReactDebugInstanceMap.isRegisteredInstance(inst2)).toBe(false);
+
+    ReactDebugInstanceMap.unregisterInstance(inst1);
+    expect(ReactDebugInstanceMap.isRegisteredInstance(inst1)).toBe(false);
+    expect(ReactDebugInstanceMap.isRegisteredInstance(inst2)).toBe(false);
+  });
+
+  it('should assign stable IDs', function() {
+    var inst1 = createStubInstance();
+    var inst2 = createStubInstance();
+
+    var inst1ID = ReactDebugInstanceMap.getIDForInstance(inst1);
+    var inst2ID = ReactDebugInstanceMap.getIDForInstance(inst2);
+    expect(typeof inst1ID).toBe('string');
+    expect(typeof inst2ID).toBe('string');
+    expect(inst1ID).not.toBe(inst2ID);
+
+    ReactDebugInstanceMap.registerInstance(inst1);
+    ReactDebugInstanceMap.registerInstance(inst2);
+    expect(ReactDebugInstanceMap.getIDForInstance(inst1)).toBe(inst1ID);
+    expect(ReactDebugInstanceMap.getIDForInstance(inst2)).toBe(inst2ID);
+
+    ReactDebugInstanceMap.unregisterInstance(inst1);
+    ReactDebugInstanceMap.unregisterInstance(inst2);
+    expect(ReactDebugInstanceMap.getIDForInstance(inst1)).toBe(inst1ID);
+    expect(ReactDebugInstanceMap.getIDForInstance(inst2)).toBe(inst2ID);
+  });
+
+  it('should retrieve registered instance by its ID', function() {
+    var inst1 = createStubInstance();
+    var inst2 = createStubInstance();
+
+    var inst1ID = ReactDebugInstanceMap.getIDForInstance(inst1);
+    var inst2ID = ReactDebugInstanceMap.getIDForInstance(inst2);
+    expect(ReactDebugInstanceMap.getInstanceByID(inst1ID)).toBe(null);
+    expect(ReactDebugInstanceMap.getInstanceByID(inst2ID)).toBe(null);
+
+    ReactDebugInstanceMap.registerInstance(inst1);
+    ReactDebugInstanceMap.registerInstance(inst2);
+    expect(ReactDebugInstanceMap.getInstanceByID(inst1ID)).toBe(inst1);
+    expect(ReactDebugInstanceMap.getInstanceByID(inst2ID)).toBe(inst2);
+
+    ReactDebugInstanceMap.unregisterInstance(inst1);
+    ReactDebugInstanceMap.unregisterInstance(inst2);
+    expect(ReactDebugInstanceMap.getInstanceByID(inst1ID)).toBe(null);
+    expect(ReactDebugInstanceMap.getInstanceByID(inst2ID)).toBe(null);
+  });
+
+  it('should warn when registering an instance twice', function() {
+    spyOn(console, 'error');
+
+    var inst = createStubInstance();
+    ReactDebugInstanceMap.registerInstance(inst);
+    expect(console.error.argsForCall.length).toBe(0);
+
+    ReactDebugInstanceMap.registerInstance(inst);
+    expect(console.error.argsForCall.length).toBe(1);
+    expect(console.error.argsForCall[0][0]).toContain(
+      'There is an internal error in the React developer tools integration. ' +
+      'A registered instance should not be registered again. ' +
+      'Please report this as a bug in React.'
+    );
+
+    ReactDebugInstanceMap.unregisterInstance(inst);
+    ReactDebugInstanceMap.registerInstance(inst);
+    expect(console.error.argsForCall.length).toBe(1);
+  });
+
+  it('should warn when unregistering an instance twice', function() {
+    spyOn(console, 'error');
+    var inst = createStubInstance();
+
+    ReactDebugInstanceMap.unregisterInstance(inst);
+    expect(console.error.argsForCall.length).toBe(1);
+    expect(console.error.argsForCall[0][0]).toContain(
+      'There is an internal error in the React developer tools integration. ' +
+      'An unregistered instance should not be unregistered again. ' +
+      'Please report this as a bug in React.'
+    );
+
+    ReactDebugInstanceMap.registerInstance(inst);
+    ReactDebugInstanceMap.unregisterInstance(inst);
+    expect(console.error.argsForCall.length).toBe(1);
+
+    ReactDebugInstanceMap.unregisterInstance(inst);
+    expect(console.error.argsForCall.length).toBe(2);
+    expect(console.error.argsForCall[1][0]).toContain(
+      'There is an internal error in the React developer tools integration. ' +
+      'An unregistered instance should not be unregistered again. ' +
+      'Please report this as a bug in React.'
+    );
+  });
+
+  it('should warn about anything than is not an internal instance', function() {
+    class Foo extends React.Component {
+      render() {
+        return <div />;
+      }
+    }
+
+    spyOn(console, 'error');
+    var warningCount = 0;
+    var div = document.createElement('div');
+    var publicInst = ReactDOM.render(<Foo />, div);
+
+    [false, null, undefined, {}, div, publicInst].forEach(falsyValue => {
+      ReactDebugInstanceMap.registerInstance(falsyValue);
+      warningCount++;
+      expect(ReactDebugInstanceMap.getIDForInstance(falsyValue)).toBe(null);
+      warningCount++;
+      expect(ReactDebugInstanceMap.isRegisteredInstance(falsyValue)).toBe(false);
+      warningCount++;
+      ReactDebugInstanceMap.unregisterInstance(falsyValue);
+      warningCount++;
+    });
+
+    expect(console.error.argsForCall.length).toBe(warningCount);
+    for (var i = 0; i < warningCount.length; i++) {
+      // Ideally we could check for the more detailed error message here
+      // but it depends on the input type and is meant for internal bugs
+      // anyway so I don't think it's worth complicating the test with it.
+      expect(console.error.argsForCall[i][0]).toContain(
+        'There is an internal error in the React developer tools integration.'
+      );
+    }
+  });
+});