diff --git a/src/isomorphic/classic/element/ReactElement.js b/src/isomorphic/classic/element/ReactElement.js
index 4e815449247af..98af361b097ba 100644
--- a/src/isomorphic/classic/element/ReactElement.js
+++ b/src/isomorphic/classic/element/ReactElement.js
@@ -398,4 +398,6 @@ ReactElement.isValidElement = function(object) {
   );
 };
 
+ReactElement.REACT_ELEMENT_TYPE = REACT_ELEMENT_TYPE;
+
 module.exports = ReactElement;
diff --git a/src/isomorphic/classic/element/ReactElementValidator.js b/src/isomorphic/classic/element/ReactElementValidator.js
index 2b7e9da3d56ad..4d4121f9810c3 100644
--- a/src/isomorphic/classic/element/ReactElementValidator.js
+++ b/src/isomorphic/classic/element/ReactElementValidator.js
@@ -184,7 +184,8 @@ function validatePropTypes(element) {
 var ReactElementValidator = {
 
   createElement: function(type, props, children) {
-    var validType = typeof type === 'string' || typeof type === 'function';
+    var validType = typeof type === 'string' || typeof type === 'function' ||
+                    (type !== null && typeof type === 'object');
     // We warn in this case but don't throw. We expect the element creation to
     // succeed and there will likely be errors in render.
     warning(
diff --git a/src/renderers/noop/__tests__/ReactNoop-test.js b/src/renderers/noop/__tests__/ReactNoop-test.js
index b71978e2cd75b..1ce47ee5c2dca 100644
--- a/src/renderers/noop/__tests__/ReactNoop-test.js
+++ b/src/renderers/noop/__tests__/ReactNoop-test.js
@@ -13,11 +13,14 @@
 
 var React;
 var ReactNoop;
+var ReactCoroutine;
 
 describe('ReactComponent', function() {
   beforeEach(function() {
     React = require('React');
     ReactNoop = require('ReactNoop');
+    ReactCoroutine = require('ReactCoroutine');
+    spyOn(console, 'log');
   });
 
   it('should render a simple component', function() {
@@ -38,11 +41,14 @@ describe('ReactComponent', function() {
   it('should render a simple component, in steps if needed', function() {
 
     function Bar() {
-      return <div>Hello World</div>;
+      return <span><div>Hello World</div></span>;
     }
 
     function Foo() {
-      return <Bar isBar={true} />;
+      return [
+        <Bar isBar={true} />,
+        <Bar isBar={true} />,
+      ];
     }
 
     ReactNoop.render(<Foo />);
@@ -53,5 +59,47 @@ describe('ReactComponent', function() {
     // console.log('Done');
   });
 
+  it('should render a coroutine', function() {
+
+    function Continuation({ isSame }) {
+      return <span>{isSame ? 'foo==bar' : 'foo!=bar'}</span>;
+    }
+
+    // An alternative API could mark Continuation as something that needs
+    // yielding. E.g. Continuation.yieldType = 123;
+    function Child({ bar }) {
+      return ReactCoroutine.createYield({
+        bar: bar,
+      }, Continuation, null);
+    }
+
+    function Indirection() {
+      return [<Child bar={true} />, <Child bar={false} />];
+    }
+
+    function HandleYields(props, yields) {
+      return yields.map(y =>
+        <y.continuation isSame={props.foo === y.props.bar} />
+      );
+    }
+
+    // An alternative API could mark Parent as something that needs
+    // yielding. E.g. Parent.handler = HandleYields;
+    function Parent(props) {
+      return ReactCoroutine.createCoroutine(
+        props.children,
+        HandleYields,
+        props
+      );
+    }
+
+    function App() {
+      return <div><Parent foo={true}><Indirection /></Parent></div>;
+    }
+
+    ReactNoop.render(<App />);
+    ReactNoop.flush();
+
+  });
 
 });
diff --git a/src/renderers/shared/fiber/ReactChildFiber.js b/src/renderers/shared/fiber/ReactChildFiber.js
new file mode 100644
index 0000000000000..bbb666cab0903
--- /dev/null
+++ b/src/renderers/shared/fiber/ReactChildFiber.js
@@ -0,0 +1,129 @@
+/**
+ * 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.
+ *
+ * @providesModule ReactChildFiber
+ * @flow
+ */
+
+'use strict';
+
+import type { ReactCoroutine, ReactYield } from 'ReactCoroutine';
+import type { Fiber } from 'ReactFiber';
+
+import type { ReactNodeList } from 'ReactTypes';
+
+var {
+  REACT_ELEMENT_TYPE,
+} = require('ReactElement');
+var {
+  REACT_COROUTINE_TYPE,
+  REACT_YIELD_TYPE,
+} = require('ReactCoroutine');
+
+var ReactFiber = require('ReactFiber');
+var ReactReifiedYield = require('ReactReifiedYield');
+
+function createSubsequentChild(parent : Fiber, previousSibling : Fiber, newChildren) : Fiber {
+  if (typeof newChildren !== 'object' || newChildren === null) {
+    return previousSibling;
+  }
+
+  switch (newChildren.$$typeof) {
+    case REACT_ELEMENT_TYPE: {
+      const element = (newChildren : ReactElement);
+      const child = ReactFiber.createFiberFromElement(element);
+      previousSibling.sibling = child;
+      child.parent = parent;
+      return child;
+    }
+
+    case REACT_COROUTINE_TYPE: {
+      const coroutine = (newChildren : ReactCoroutine);
+      const child = ReactFiber.createFiberFromCoroutine(coroutine);
+      previousSibling.sibling = child;
+      child.parent = parent;
+      return child;
+    }
+
+    case REACT_YIELD_TYPE: {
+      const yieldNode = (newChildren : ReactYield);
+      const reifiedYield = ReactReifiedYield.createReifiedYield(yieldNode);
+      const child = ReactFiber.createFiberFromYield(yieldNode);
+      child.output = reifiedYield;
+      previousSibling.sibling = child;
+      child.parent = parent;
+      return child;
+    }
+  }
+
+  if (Array.isArray(newChildren)) {
+    let prev : Fiber = previousSibling;
+    for (var i = 0; i < newChildren.length; i++) {
+      prev = createSubsequentChild(parent, prev, newChildren[i]);
+    }
+    return prev;
+  } else {
+    console.log('Unknown child', newChildren);
+    return previousSibling;
+  }
+}
+
+function createFirstChild(parent, newChildren) {
+  if (typeof newChildren !== 'object' || newChildren === null) {
+    return null;
+  }
+
+  switch (newChildren.$$typeof) {
+    case REACT_ELEMENT_TYPE: {
+      const element = (newChildren : ReactElement);
+      const child = ReactFiber.createFiberFromElement(element);
+      child.parent = parent;
+      return child;
+    }
+
+    case REACT_COROUTINE_TYPE: {
+      const coroutine = (newChildren : ReactCoroutine);
+      const child = ReactFiber.createFiberFromCoroutine(coroutine);
+      child.parent = parent;
+      return child;
+    }
+
+    case REACT_YIELD_TYPE: {
+      // A yield results in a fragment fiber whose output is the continuation.
+      // TODO: When there is only a single child, we can optimize this to avoid
+      // the fragment.
+      const yieldNode = (newChildren : ReactYield);
+      const reifiedYield = ReactReifiedYield.createReifiedYield(yieldNode);
+      const child = ReactFiber.createFiberFromYield(yieldNode);
+      child.output = reifiedYield;
+      child.parent = parent;
+      return child;
+    }
+  }
+
+  if (Array.isArray(newChildren)) {
+    var first : ?Fiber = null;
+    var prev : ?Fiber = null;
+    for (var i = 0; i < newChildren.length; i++) {
+      if (prev == null) {
+        prev = createFirstChild(parent, newChildren[i]);
+        first = prev;
+      } else {
+        prev = createSubsequentChild(parent, prev, newChildren[i]);
+      }
+    }
+    return first;
+  } else {
+    console.log('Unknown child', newChildren);
+    return null;
+  }
+}
+
+exports.reconcileChildFibers = function(parent : Fiber, firstChild : ?Fiber, newChildren : ReactNodeList) : ?Fiber {
+  return createFirstChild(parent, newChildren);
+};
diff --git a/src/renderers/shared/fiber/ReactFiber.js b/src/renderers/shared/fiber/ReactFiber.js
index 9e99e8998c6ba..eb17068b6c024 100644
--- a/src/renderers/shared/fiber/ReactFiber.js
+++ b/src/renderers/shared/fiber/ReactFiber.js
@@ -12,31 +12,47 @@
 
 'use strict';
 
-type StateNode = {};
-type EffectHandler = () => void;
-type EffectTag = number;
+var ReactTypesOfWork = require('ReactTypesOfWork');
+var {
+  IndeterminateComponent,
+  ClassComponent,
+  HostComponent,
+  CoroutineComponent,
+  YieldComponent,
+} = ReactTypesOfWork;
+
+var ReactElement = require('ReactElement');
+
+import type { ReactCoroutine, ReactYield } from 'ReactCoroutine';
 
 export type Fiber = {
 
+  // Tag identifying the type of fiber.
   tag: number,
 
-  parent: ?Fiber,
+  // Singly Linked List Tree Structure.
+  parent: ?Fiber, // Consider a regenerated temporary parent stack instead.
   child: ?Fiber,
   sibling: ?Fiber,
 
-  input: ?Object,
-  output: ?Object,
+  // Input is the data coming into process this fiber. Arguments.
+  input: any, // This type will be more specific once we overload the tag.
+  // Output is the return value of this fiber, or a linked list of return values
+  // if this returns multiple values. Such as a fragment.
+  output: any, // This type will be more specific once we overload the tag.
 
-  handler: EffectHandler,
-  handlerTag: EffectTag,
+  // Used by multi-stage coroutines.
+  stage: number, // Consider reusing the tag field instead.
 
+  // This will be used to quickly determine if a subtree has no pending changes.
   hasPendingChanges: bool,
 
-  stateNode: StateNode,
+  // The local state associated with this fiber.
+  stateNode: ?Object,
 
 };
 
-module.exports = function(tag : number) : Fiber {
+var createFiber = function(tag : number) : Fiber {
   return {
 
     tag: tag,
@@ -48,12 +64,53 @@ module.exports = function(tag : number) : Fiber {
     input: null,
     output: null,
 
-    handler: function() {},
-    handlerTag: 0,
+    stage: 0,
 
     hasPendingChanges: true,
 
-    stateNode: {},
+    stateNode: null,
 
   };
 };
+
+function shouldConstruct(Component) {
+  return !!(Component.prototype && Component.prototype.isReactComponent);
+}
+
+exports.createFiberFromElement = function(element : ReactElement) {
+  const fiber = exports.createFiberFromElementType(element.type);
+  if (typeof element.type === 'object') {
+    // Hacky McHack
+    element = ReactElement(fiber.input, null, element.ref, null, null, null, element.props);
+  }
+  fiber.input = element;
+  return fiber;
+};
+
+exports.createFiberFromElementType = function(type : mixed) {
+  let fiber;
+  if (typeof type === 'function') {
+    fiber = shouldConstruct(type) ?
+      createFiber(ClassComponent) :
+      createFiber(IndeterminateComponent);
+  } else if (typeof type === 'string') {
+    fiber = createFiber(HostComponent);
+  } else if (typeof type === 'object' && type !== null) {
+    // Currently assumed to be a continuation and therefore is a fiber already.
+    fiber = type;
+  } else {
+    throw new Error('Unknown component type: ' + typeof type);
+  }
+  return fiber;
+};
+
+exports.createFiberFromCoroutine = function(coroutine : ReactCoroutine) {
+  const fiber = createFiber(CoroutineComponent);
+  fiber.input = coroutine;
+  return fiber;
+};
+
+exports.createFiberFromYield = function(yieldNode : ReactYield) {
+  const fiber = createFiber(YieldComponent);
+  return fiber;
+};
diff --git a/src/renderers/shared/fiber/ReactFiberBeginWork.js b/src/renderers/shared/fiber/ReactFiberBeginWork.js
new file mode 100644
index 0000000000000..19026242f9ec3
--- /dev/null
+++ b/src/renderers/shared/fiber/ReactFiberBeginWork.js
@@ -0,0 +1,134 @@
+/**
+ * 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.
+ *
+ * @providesModule ReactFiberBeginWork
+ * @flow
+ */
+
+'use strict';
+
+import type { ReactCoroutine } from 'ReactCoroutine';
+import type { Fiber } from 'ReactFiber';
+
+var ReactChildFiber = require('ReactChildFiber');
+var ReactTypesOfWork = require('ReactTypesOfWork');
+var {
+  IndeterminateComponent,
+  FunctionalComponent,
+  ClassComponent,
+  HostComponent,
+  CoroutineComponent,
+  YieldComponent,
+} = ReactTypesOfWork;
+
+function getElement(unitOfWork) : ReactElement {
+  var element = unitOfWork.input;
+  if (!element) {
+    throw new Error('Should be resolved by now');
+  }
+  return (element : ReactElement);
+}
+
+function updateFunctionalComponent(unitOfWork) {
+  var element = getElement(unitOfWork);
+  var fn = element.type;
+  var props = element.props;
+  console.log('perform work on:', fn.name);
+  var nextChildren = fn(props);
+
+  unitOfWork.child = ReactChildFiber.reconcileChildFibers(
+    unitOfWork,
+    unitOfWork.child,
+    nextChildren
+  );
+}
+
+function updateHostComponent(unitOfWork) {
+  var element = getElement(unitOfWork);
+  console.log('host component', element.type, typeof element.props.children === 'string' ? element.props.children : '');
+
+  var nextChildren = element.props.children;
+  unitOfWork.child = ReactChildFiber.reconcileChildFibers(
+    unitOfWork,
+    unitOfWork.child,
+    nextChildren
+  );
+}
+
+function mountIndeterminateComponent(unitOfWork) {
+  var element = getElement(unitOfWork);
+  var fn = element.type;
+  var props = element.props;
+  var value = fn(props);
+  if (typeof value === 'object' && value && typeof value.render === 'function') {
+    console.log('performed work on class:', fn.name);
+    // Proceed under the assumption that this is a class instance
+    unitOfWork.tag = ClassComponent;
+  } else {
+    console.log('performed work on fn:', fn.name);
+    // Proceed under the assumption that this is a functional component
+    unitOfWork.tag = FunctionalComponent;
+  }
+  unitOfWork.child = ReactChildFiber.reconcileChildFibers(
+    unitOfWork,
+    unitOfWork.child,
+    value
+  );
+}
+
+function updateCoroutineComponent(unitOfWork) {
+  var coroutine = (unitOfWork.input : ?ReactCoroutine);
+  if (!coroutine) {
+    throw new Error('Should be resolved by now');
+  }
+  console.log('begin coroutine', coroutine.handler.name);
+  unitOfWork.child = ReactChildFiber.reconcileChildFibers(
+    unitOfWork,
+    unitOfWork.child,
+    coroutine.children
+  );
+}
+
+function beginWork(unitOfWork : Fiber) : ?Fiber {
+  switch (unitOfWork.tag) {
+    case IndeterminateComponent:
+      mountIndeterminateComponent(unitOfWork);
+      break;
+    case FunctionalComponent:
+      updateFunctionalComponent(unitOfWork);
+      break;
+    case ClassComponent:
+      console.log('class component', unitOfWork.input.type.name);
+      break;
+    case HostComponent:
+      updateHostComponent(unitOfWork);
+      break;
+    case CoroutineComponent:
+      // Reset the stage to zero.
+      unitOfWork.stage = 0;
+      updateCoroutineComponent(unitOfWork);
+      // This doesn't take arbitrary time so we could synchronously just begin
+      // eagerly do the work of unitOfWork.child as an optimization.
+      if (unitOfWork.child) {
+        return beginWork(unitOfWork.child);
+      }
+      break;
+    case YieldComponent:
+      // A yield component is just a placeholder, we can just run through the
+      // next one immediately.
+      if (unitOfWork.sibling) {
+        return beginWork(unitOfWork.sibling);
+      }
+      return null;
+    default:
+      throw new Error('Unknown unit of work tag');
+  }
+  return unitOfWork.child;
+}
+
+exports.beginWork = beginWork;
diff --git a/src/renderers/shared/fiber/ReactFiberCompleteWork.js b/src/renderers/shared/fiber/ReactFiberCompleteWork.js
new file mode 100644
index 0000000000000..827075f004312
--- /dev/null
+++ b/src/renderers/shared/fiber/ReactFiberCompleteWork.js
@@ -0,0 +1,121 @@
+/**
+ * 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.
+ *
+ * @providesModule ReactFiberCompleteWork
+ * @flow
+ */
+
+'use strict';
+
+import type { ReactCoroutine } from 'ReactCoroutine';
+import type { Fiber } from 'ReactFiber';
+
+import type { ReifiedYield } from 'ReactReifiedYield';
+
+var ReactChildFiber = require('ReactChildFiber');
+var ReactTypesOfWork = require('ReactTypesOfWork');
+var {
+  IndeterminateComponent,
+  FunctionalComponent,
+  ClassComponent,
+  HostComponent,
+  CoroutineComponent,
+  YieldComponent,
+} = ReactTypesOfWork;
+
+function transferOutput(child : ?Fiber, parent : Fiber) {
+  // If we have a single result, we just pass that through as the output to
+  // avoid unnecessary traversal. When we have multiple output, we just pass
+  // the linked list of fibers that has the individual output values.
+  parent.output = (child && !child.sibling) ? child.output : child;
+}
+
+function recursivelyFillYields(yields, output : ?Fiber | ?ReifiedYield) {
+  if (!output) {
+    // Ignore nulls etc.
+  } else if (output.tag !== undefined) { // TODO: Fix this fragile duck test.
+    // Detect if this is a fiber, if so it is a fragment result.
+    // $FlowFixMe: Refinement issue.
+    var item = (output : Fiber);
+    do {
+      recursivelyFillYields(yields, item.output);
+      item = item.sibling;
+    } while (item);
+  } else {
+    // $FlowFixMe: Refinement issue. If it is not a Fiber or null, it is a yield
+    yields.push(output);
+  }
+}
+
+function handleCoroutine(unitOfWork : Fiber) {
+  var coroutine = (unitOfWork.input : ?ReactCoroutine);
+  if (!coroutine) {
+    throw new Error('Should be resolved by now');
+  }
+
+  if (unitOfWork.stage === 0) {
+    // First step of the coroutine has completed. Now we need to do the second.
+    // TODO: It would be nice to have a multi stage coroutine represented by a
+    // single component, or at least tail call optimize nested ones.
+    // TODO: If we end up not using multi stage coroutines, we could also reuse
+    // the tag field to switch between the two stages.
+    unitOfWork.stage = 1;
+
+    // Build up the yields.
+    // TODO: Compare this to a generator or opaque helpers like Children.
+    var yields : Array<ReifiedYield> = [];
+    var child = unitOfWork.child;
+    while (child) {
+      recursivelyFillYields(yields, child.output);
+      child = child.sibling;
+    }
+    var fn = coroutine.handler;
+    var props = coroutine.props;
+    var nextChildren = fn(props, yields);
+
+    unitOfWork.stateNode = ReactChildFiber.reconcileChildFibers(
+      unitOfWork,
+      unitOfWork.stateNode,
+      nextChildren
+    );
+    return unitOfWork.stateNode;
+  } else {
+    // The coroutine is now complete.
+    transferOutput(unitOfWork.stateNode, unitOfWork);
+    return null;
+  }
+}
+
+exports.completeWork = function(unitOfWork : Fiber) : ?Fiber {
+  switch (unitOfWork.tag) {
+    case FunctionalComponent:
+      console.log('/functional component', unitOfWork.input.type.name);
+      transferOutput(unitOfWork.child, unitOfWork);
+      break;
+    case ClassComponent:
+      console.log('/class component', unitOfWork.input.type.name);
+      transferOutput(unitOfWork.child, unitOfWork);
+      break;
+    case HostComponent:
+      console.log('/host component', unitOfWork.input.type);
+      break;
+    case CoroutineComponent:
+      console.log('/coroutine component', unitOfWork.input.handler.name);
+      return handleCoroutine(unitOfWork);
+    case YieldComponent:
+      // Does nothing.
+      break;
+
+    // Error cases
+    case IndeterminateComponent:
+      throw new Error('An indeterminate component should have become determinate before completing.');
+    default:
+      throw new Error('Unknown unit of work tag');
+  }
+  return null;
+};
diff --git a/src/renderers/shared/fiber/ReactFiberFunctionalComponent.js b/src/renderers/shared/fiber/ReactFiberFunctionalComponent.js
deleted file mode 100644
index 8c5ac48f8c06f..0000000000000
--- a/src/renderers/shared/fiber/ReactFiberFunctionalComponent.js
+++ /dev/null
@@ -1,45 +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.
- *
- * @providesModule ReactFiberFunctionalComponent
- * @flow
- */
-
-'use strict';
-
-import type { Fiber } from 'ReactFiber';
-var createFiber = require('ReactFiber');
-
-var ReactTypesOfWork = require('ReactTypesOfWork');
-var {
-  FunctionalComponent,
-} = ReactTypesOfWork;
-
-exports.performWork = function(unitOfWork : Fiber) : ?Fiber {
-  var element = unitOfWork.input;
-  if (!element) {
-    throw new Error('Should be resolved by now');
-  }
-  var fn = element.type;
-  var props = element.props;
-  // console.log('perform work on:', fn.name);
-  var nextElement = fn(props);
-
-  if (typeof nextElement.type === 'function') {
-    return exports.createFiber(nextElement);
-  }
-  return null;
-};
-
-exports.createFiber = function(element : ReactElement) {
-  var fiber = createFiber(
-    FunctionalComponent
-  );
-  fiber.input = element;
-  return fiber;
-};
diff --git a/src/renderers/shared/fiber/ReactFiberReconciler.js b/src/renderers/shared/fiber/ReactFiberReconciler.js
index 3ef59bdb5e163..4a13a6531bca5 100644
--- a/src/renderers/shared/fiber/ReactFiberReconciler.js
+++ b/src/renderers/shared/fiber/ReactFiberReconciler.js
@@ -13,14 +13,9 @@
 'use strict';
 
 import type { Fiber } from 'ReactFiber';
-var ReactFiberFunctionalComponent = require('ReactFiberFunctionalComponent');
-
-var ReactTypesOfWork = require('ReactTypesOfWork');
-var {
-  FunctionalComponent,
-  ClassComponent,
-  HostComponent,
-} = ReactTypesOfWork;
+var ReactFiber = require('ReactFiber');
+var { beginWork } = require('ReactFiberBeginWork');
+var { completeWork } = require('ReactFiberCompleteWork');
 
 type ReactHostElement<T, P> = {
   type: T,
@@ -54,16 +49,34 @@ module.exports = function<T, P, I>(config : HostConfig<T, P, I>) : Reconciler {
 
   let nextUnitOfWork : ?Fiber = null;
 
-  function performUnitOfWork(unit : Fiber) : ?Fiber {
-    switch (unit.tag) {
-      case FunctionalComponent:
-        return ReactFiberFunctionalComponent.performWork(unit);
-      case ClassComponent:
-        break;
-      case HostComponent:
-        break;
+  function completeUnitOfWork(unitOfWork : Fiber) : ?Fiber {
+    while (true) {
+      var next = completeWork(unitOfWork);
+      if (next) {
+        // If completing this work spawned new work, do that next.
+        return next;
+      } else if (unitOfWork.sibling) {
+        // If there is more work to do in this parent, do that next.
+        return unitOfWork.sibling;
+      } else if (unitOfWork.parent) {
+        // If there's no more work in this parent. Complete the parent.
+        unitOfWork = unitOfWork.parent;
+      } else {
+        // If we're at the root, there's no more work to do.
+        return null;
+      }
+    }
+  }
+
+  function performUnitOfWork(unitOfWork : Fiber) : ?Fiber {
+    var next = beginWork(unitOfWork);
+    if (next) {
+      // If this spawns new work, do that next.
+      return next;
+    } else {
+      // Otherwise, complete the current work.
+      return completeUnitOfWork(unitOfWork);
     }
-    return null;
   }
 
   function performLowPriWork(deadline : Deadline) {
@@ -100,7 +113,7 @@ module.exports = function<T, P, I>(config : HostConfig<T, P, I>) : Reconciler {
 
       ensureLowPriIsScheduled();
 
-      nextUnitOfWork = ReactFiberFunctionalComponent.createFiber(element);
+      nextUnitOfWork = ReactFiber.createFiberFromElement(element);
 
       return {};
     },
diff --git a/src/renderers/shared/fiber/ReactReifiedYield.js b/src/renderers/shared/fiber/ReactReifiedYield.js
new file mode 100644
index 0000000000000..a47887bc56ba1
--- /dev/null
+++ b/src/renderers/shared/fiber/ReactReifiedYield.js
@@ -0,0 +1,37 @@
+/**
+ * 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.
+ *
+ * @providesModule ReactReifiedYield
+ * @flow
+ */
+
+'use strict';
+
+import type { ReactYield } from 'ReactCoroutine';
+import type { Fiber } from 'ReactFiber';
+
+var ReactFiber = require('ReactFiber');
+
+export type ReifiedYield = { continuation: Fiber, props: Object };
+
+exports.createReifiedYield = function(yieldNode : ReactYield) : ReifiedYield {
+  var fiber = ReactFiber.createFiberFromElementType(yieldNode.continuation);
+  // Hacky way to store the continuation
+  fiber.input = yieldNode.continuation;
+  return {
+    continuation: fiber,
+    props: yieldNode.props,
+  };
+};
+
+exports.createUpdatedReifiedYield = function(previousYield : ReifiedYield, yieldNode : ReactYield) : ReifiedYield {
+  return {
+    continuation: previousYield.continuation,
+    props: yieldNode.props,
+  };
+};
diff --git a/src/renderers/shared/fiber/ReactStateNode.js b/src/renderers/shared/fiber/ReactStateNode.js
deleted file mode 100644
index c7ea45b3b4064..0000000000000
--- a/src/renderers/shared/fiber/ReactStateNode.js
+++ /dev/null
@@ -1,23 +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.
- *
- * @providesModule ReactStateNode
- * @flow
- */
-
-'use strict';
-
-type StateNode = {
-  next: ?{ [key: string]: StateNode },
-};
-
-module.exports = function() : StateNode {
-  return {
-    next: null,
-  };
-};
diff --git a/src/renderers/shared/fiber/ReactTypesOfWork.js b/src/renderers/shared/fiber/ReactTypesOfWork.js
index 5dda9346102f0..5009cfa6bcb5b 100644
--- a/src/renderers/shared/fiber/ReactTypesOfWork.js
+++ b/src/renderers/shared/fiber/ReactTypesOfWork.js
@@ -13,9 +13,12 @@
 'use strict';
 
 var TypesOfWork = {
+  IndeterminateComponent: 0, // Before we know whether it is functional or class
   FunctionalComponent: 1,
   ClassComponent: 2,
   HostComponent: 3,
+  CoroutineComponent: 4,
+  YieldComponent: 5,
 };
 
 module.exports = TypesOfWork;
diff --git a/src/renderers/shared/fiber/isomorphic/ReactCoroutine.js b/src/renderers/shared/fiber/isomorphic/ReactCoroutine.js
new file mode 100644
index 0000000000000..a03934ea56fcd
--- /dev/null
+++ b/src/renderers/shared/fiber/isomorphic/ReactCoroutine.js
@@ -0,0 +1,109 @@
+/**
+ * Copyright 2014-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 ReactCoroutine
+ * @flow
+ */
+
+'use strict';
+
+import type { ReactNodeList } from 'ReactTypes';
+
+// The Symbol used to tag the special React types. If there is no native Symbol
+// nor polyfill, then a plain number is used for performance.
+var REACT_COROUTINE_TYPE =
+  (typeof Symbol === 'function' && Symbol.for && Symbol.for('react.coroutine')) ||
+  0xeac8;
+
+var REACT_YIELD_TYPE =
+  (typeof Symbol === 'function' && Symbol.for && Symbol.for('react.yield')) ||
+  0xeac9;
+
+type ReifiedYield = { continuation: Object, props: Object };
+type CoroutineHandler<T> = (props: T, yields: Array<ReifiedYield>) => ReactNodeList;
+
+export type ReactCoroutine = {
+  $$typeof: Symbol | number,
+  key: ?string,
+  children: any,
+  // This should be a more specific CoroutineHandler
+  handler: (props: any, yields: Array<ReifiedYield>) => ReactNodeList,
+  props: mixed,
+};
+export type ReactYield = {
+  $$typeof: Symbol | number,
+  key: ?string,
+  props: Object,
+  continuation: mixed
+};
+
+exports.createCoroutine = function<T>(children : mixed, handler : CoroutineHandler<T>, props : T, key : ?string = null) : ReactCoroutine {
+  var coroutine = {
+    // This tag allow us to uniquely identify this as a React Coroutine
+    $$typeof: REACT_COROUTINE_TYPE,
+    key: key == null ? null : '' + key,
+    children: children,
+    handler: handler,
+    props: props,
+  };
+
+  if (__DEV__) {
+    // TODO: Add _store property for marking this as validated.
+    if (Object.freeze) {
+      Object.freeze(coroutine.props);
+      Object.freeze(coroutine);
+    }
+  }
+
+  return coroutine;
+};
+
+exports.createYield = function(props : mixed, continuation : mixed, key : ?string = null) {
+  var yieldNode = {
+    // This tag allow us to uniquely identify this as a React Yield
+    $$typeof: REACT_YIELD_TYPE,
+    key: key == null ? null : '' + key,
+    props: props,
+    continuation: continuation,
+  };
+
+  if (__DEV__) {
+    // TODO: Add _store property for marking this as validated.
+    if (Object.freeze) {
+      Object.freeze(yieldNode.props);
+      Object.freeze(yieldNode);
+    }
+  }
+
+  return yieldNode;
+};
+
+/**
+ * Verifies the object is a coroutine object.
+ */
+exports.isCoroutine = function(object : mixed) : boolean {
+  return (
+    typeof object === 'object' &&
+    object !== null &&
+    object.$$typeof === REACT_COROUTINE_TYPE
+  );
+};
+
+/**
+ * Verifies the object is a yield object.
+ */
+exports.isYield = function(object : mixed) : boolean {
+  return (
+    typeof object === 'object' &&
+    object !== null &&
+    object.$$typeof === REACT_YIELD_TYPE
+  );
+};
+
+exports.REACT_YIELD_TYPE = REACT_YIELD_TYPE;
+exports.REACT_COROUTINE_TYPE = REACT_COROUTINE_TYPE;
diff --git a/src/renderers/shared/fiber/isomorphic/ReactTypes.js b/src/renderers/shared/fiber/isomorphic/ReactTypes.js
new file mode 100644
index 0000000000000..4c8c69571c222
--- /dev/null
+++ b/src/renderers/shared/fiber/isomorphic/ReactTypes.js
@@ -0,0 +1,25 @@
+/**
+ * Copyright 2014-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 ReactTypes
+ * @flow
+ */
+
+'use strict';
+
+import type { ReactCoroutine, ReactYield } from 'ReactCoroutine';
+
+export type ReactNode = ReactElement | ReactCoroutine | ReactYield | ReactText | ReactFragment;
+
+export type ReactFragment = ReactEmpty | Iterable<ReactNode>;
+
+export type ReactNodeList = ReactEmpty | ReactNode;
+
+export type ReactText = string | number;
+
+export type ReactEmpty = null | void | boolean;
diff --git a/src/renderers/shared/stack/reconciler/__tests__/ReactComponent-test.js b/src/renderers/shared/stack/reconciler/__tests__/ReactComponent-test.js
index f97ae25c09776..cd0c13d6e5f92 100644
--- a/src/renderers/shared/stack/reconciler/__tests__/ReactComponent-test.js
+++ b/src/renderers/shared/stack/reconciler/__tests__/ReactComponent-test.js
@@ -280,14 +280,8 @@ describe('ReactComponent', function() {
       'or a class/function (for composite components) but got: null.'
     );
 
-    var Z = {};
-    expect(() => ReactTestUtils.renderIntoDocument(<Z />)).toThrowError(
-      'Element type is invalid: expected a string (for built-in components) ' +
-      'or a class/function (for composite components) but got: object.'
-    );
-
     // One warning for each element creation
-    expect(console.error.calls.count()).toBe(3);
+    expect(console.error.calls.count()).toBe(2);
   });
 
 });