diff --git a/interpreter.js b/interpreter.js
index fefc311..00b0251 100644
--- a/interpreter.js
+++ b/interpreter.js
@@ -433,6 +433,59 @@ Interpreter.prototype.run = function() {
   return this.paused_;
 };
 
+/**
+ * Queue a pseudo function for execution on next step
+ * @param {Interpreter.Object} func Interpreted function
+ * @param {Interpreter.Object} funcThis Interpreted Object to use as "this"
+ * @param {Interpreter.Object} var_args Interpreted Objects to pass as arguments
+ * @return {Interpreter.Callback} Object for running pseudo function callback
+ */
+Interpreter.prototype.callFunction = function (func, funcThis, var_args) {
+  var expNode = this.buildFunctionCaller_.apply(this, arguments);
+  return new Interpreter.Callback(expNode);
+};
+
+/**
+ * Queue a pseudo function for execution after all current instructions complete
+ * @param {Interpreter.Object} func Interpreted function
+ * @param {Interpreter.Object} funcThis Interpreted Object to use as "this"
+ * @param {Interpreter.Object} var_args Interpreted Objects to pass as arguments
+ * @return {Interpreter.Callback} Object for running pseudo function callback
+ */
+Interpreter.prototype.queueFunction = function (func, funcThis, var_args) {
+  var state = this.stateStack[0];
+  var expNode = this.buildFunctionCaller_.apply(this, arguments);
+  // Add function call to root Program state
+  state.node['body'].push(expNode);
+  state.done = false;
+  return new Interpreter.Callback(expNode, true); // Allows adding then/catch
+};
+
+/**
+ * Generate state objects for running pseudo function
+ * @param {Interpreter.Object} func Interpreted function
+ * @param {Interpreter.Object} funcThis Interpreted Object to use as "this"
+ * @param {Interpreter.Object} var_args Interpreted Objects to pass as arguments
+ * @return {nodeConstructor} node for running pseudo function
+ */
+Interpreter.prototype.buildFunctionCaller_ = function (func, funcThis, var_args) {
+  var thisInterpreter = this
+  var args = Array.prototype.slice.call(arguments, 2).map(function (arg) {
+    return arg instanceof Interpreter.Object ? arg : thisInterpreter.nativeToPseudo(arg)
+  });
+  // Create node for CallExpression with pre-embedded function and arguments
+  var scope = this.stateStack[this.stateStack.length - 1].scope; // This may be wrong
+  var ceNode = new this.nodeConstructor({options:{}});
+  ceNode['type'] = 'CallExpressionFunc_';
+  // Attach state settings to node, so we can retrieve them later.
+  // (Can only add a node to root program body.)
+  ceNode.funcThis_ = funcThis;
+  ceNode.func_ = func;
+  ceNode.arguments_ = args;
+  ceNode.scope_ = scope;
+  return ceNode;
+};
+
 /**
  * Initialize the global object with buitin properties and functions.
  * @param {!Interpreter.Object} globalObject Global object.
@@ -3142,6 +3195,48 @@ Interpreter.prototype.throwException = function(errorClass, opt_message) {
   throw Interpreter.STEP_ERROR;
 };
 
+/**
+ * Return a Throwable object for use in native function return values
+ * @param {!Interpreter.Object|Interpreter.Value} errorClass Type of error
+ *   (if message is provided) or the value to throw (if no message).
+ * @param {string=} opt_message Message being thrown.
+ */
+Interpreter.prototype.createThrowable = function(errorClass, opt_message) {
+  return new Interpreter.Throwable(errorClass, opt_message);
+};
+
+/**
+ * Handle result of native function call
+ * @param {Interpreter.State} state CallExpression state
+ * @param {!Interpreter.Scope} scope CallExpression scope.
+ * @param {Interpreter.Object|String|Number} value Values returned from native function
+ * @return {Interpreter.State} New callback state added, if any
+ */
+Interpreter.prototype.handleNativeResult_ = function(state, scope, value) {
+  if (value instanceof Interpreter.Callback) {
+    // We have a request for a pseudo function callback
+    value.pushState_(this, scope);
+    state.cb_ = value;
+    state.doneExec_ = false;
+    return value.state_;
+  } else if (value instanceof Interpreter.Throwable) {
+    // Result was an error
+    value.throw_(this);
+  } else {
+    // We have a final value
+    var cb = state.cb_;
+    if (cb) {
+      if (cb.stateless_) {
+        cb.value = value;
+      } else {
+        cb.state_.value = value;
+      }
+    }
+    state.value = value;
+  }
+};
+
+
 /**
  * Unwind the stack to the innermost relevant enclosing TryStatement,
  * For/ForIn/WhileStatement or Call/NewExpression.  If this results in
@@ -3171,6 +3266,13 @@ Interpreter.prototype.unwind = function(type, value, label) {
           throw Error('Unsynatctic break/continue not rejected by Acorn');
         }
         break;
+      case 'CallExpressionFunc_':
+        if (type === Interpreter.Completion.THROW && state.catch_) {
+          // Let stepCallExpressionFunc_ catch this throw
+          state.throw_ = value;
+          return;
+        }
+        continue;
       case 'Program':
         // Don't pop the stateStack.
         // Leave the root scope on the tree in case the program is appended to.
@@ -3349,6 +3451,104 @@ Interpreter.Scope = function(parentScope, strict, object) {
   this.object = object;
 };
 
+/**
+ * Class for allowing async function throws
+ * @param {!Interpreter.Object|Interpreter.Value} errorClass Type of error
+ *   (if message is provided) or the value to throw (if no message).
+ * @param {string=} opt_message Message being thrown.
+ * @constructor
+ */
+Interpreter.Throwable = function(errorClass, opt_message) {
+  this.errorClass = errorClass;
+  this.opt_message = opt_message;
+};
+
+/**
+ * Class for allowing async function throws
+ * @param {Interpreter} interpreter Interpreter instance
+ * @constructor
+ */
+Interpreter.Throwable.prototype.throw_ = function(interpreter) {
+  interpreter.throwException(this.errorClass, this.opt_message);
+};
+
+
+/**
+ * Class for tracking native function states.
+ * @param {nodeConstructor} callFnState State that's being tracked
+ * @param {Boolean=} opt_queued Will this be queued or immediate
+ * @constructor
+ */
+Interpreter.Callback = function(callFnNode, opt_queued) {
+  this.node_ = callFnNode;
+  this.handlers_ = [];
+  this.catch_ = null;
+  this.node_.cb_ = this; // Attach callback to node so we can retrieve it later
+  this.queued_ = opt_queued;
+};
+
+/**
+ * Add handler for return of pseudo function's value
+ * @param {Function} handler Function to handle value
+ * @return {Interpreter.Callback} State object for running pseudo function
+ */
+Interpreter.Callback.prototype['then'] = function(handler) {
+  if (typeof handler !== 'function') {
+    throw new Error('Expected function for "then" handler');
+  }
+  this.handlers_.push(handler);
+  return this;
+};
+
+/**
+ * Add exception catch handler for return of pseudo function's call
+ * @param {Function} handler Function to handle value
+ * @return {Interpreter.Callback} State object for running pseudo function
+ */
+Interpreter.Callback.prototype['catch'] = function(handler) {
+  if (typeof handler !== 'function') {
+    throw new Error('Expected function for "catch" handler');
+  }
+  if (this.catch_) {
+    throw new Error('"catch" already defined');
+  }
+  // this.node_.skipThrow_ = true;
+  this.catch_ = handler;
+  return this;
+};
+
+/**
+ * Add pseudo function callback to statStack
+ * @param {Interpreter} interpreter Interpreter instance
+ * @param {Interpreter.Scope} scope Function's scope.
+ */
+Interpreter.Callback.prototype.pushState_ = function(interpreter, scope) {
+  if (this.stateless_) return; // Only uses handler_
+  if (!this.state_) {
+    this.state_ = new Interpreter.State(this.node_, scope);
+  }
+  interpreter.stateStack.push(this.state_);
+};
+
+/**
+ * Handle next step for native function callback
+ * @param {Interpreter.Object} value Object containing pseudo function callback's result.
+ * @param {Function} asyncCallback Function for asyncFunc callback
+ */
+Interpreter.Callback.prototype.doNext_ = function(asyncCallback) {
+  var handler =  this.handlers_.shift();
+  if (handler) {
+    this.force_ = this.handlers_.length; // Continue to run if we have more
+    return handler(this.stateless_ ? this.value : this.state_.value, asyncCallback);
+  }
+  if (this.stateless_) return; // Callback does not have a state value
+  if(asyncCallback) {
+    asyncCallback(this.state_.value)
+  } else {
+    return this.state_.value
+  }
+};
+
 /**
  * Class for an object.
  * @param {Interpreter.Object} proto Prototype object or null.
@@ -3712,6 +3912,11 @@ Interpreter.prototype['stepCallExpression'] = function(stack, state, node) {
     }
     state.doneArgs_ = true;
   }
+  if (state.cb_ && state.cb_.force_) {
+    // Callback wants to run again
+    state.doneExec_ = false;
+    state.cb_.force_ = false;
+  }
   if (!state.doneExec_) {
     state.doneExec_ = true;
     if (!(func instanceof Interpreter.Object)) {
@@ -3774,19 +3979,27 @@ Interpreter.prototype['stepCallExpression'] = function(stack, state, node) {
       if (!state.scope.strict) {
         state.funcThis_ = this.boxThis_(state.funcThis_);
       }
-      state.value = func.nativeFunc.apply(state.funcThis_, state.arguments_);
+      this.handleNativeResult_(state, scope, state.cb_
+        ? state.cb_.doNext_()
+        : func.nativeFunc.apply(state.funcThis_, state.arguments_));
+        return;
     } else if (func.asyncFunc) {
       var thisInterpreter = this;
       var callback = function(value) {
-        state.value = value;
         thisInterpreter.paused_ = false;
+        thisInterpreter.handleNativeResult_(state, scope, value);
       };
+      this.paused_ = true;
+      if (state.cb_) {
+        // Do next step of native async func
+        state.cb_.doNext_(callback);
+        return;
+      }
       // Force the argument lengths to match, then append the callback.
       var argLength = func.asyncFunc.length - 1;
       var argsWithCallback = state.arguments_.concat(
           new Array(argLength)).slice(0, argLength);
       argsWithCallback.push(callback);
-      this.paused_ = true;
       if (!state.scope.strict) {
         state.funcThis_ = this.boxThis_(state.funcThis_);
       }
@@ -3887,6 +4100,53 @@ Interpreter.prototype['stepEvalProgram_'] = function(stack, state, node) {
   stack[stack.length - 1].value = this.value;
 };
 
+Interpreter.prototype['stepCallExpressionFunc_'] = function(stack, state, node) {
+  var cb = node.cb_;
+  var queued = cb.queued_;
+  if (!state.done_) {
+    state.done_ = true;
+    var ceNode = new this.nodeConstructor({options:{}});
+    ceNode['type'] = 'CallExpression';
+    var ceState = new Interpreter.State(ceNode, node.scope_ || state.scope);
+    ceState.doneCallee_ = true;
+    ceState.funcThis_ = node.funcThis_;
+    ceState.func_ = node.func_;
+    ceState.doneArgs_ = true;
+    ceState.arguments_ = node.arguments_;
+    state.catch_ = cb.catch_;
+    return ceState;
+  }
+  if (queued && cb.handlers_.length && !state.throw_) {
+    // Called via queued callback
+    // Callback a 'then' handler now (non-queued are called in setCallExpression)
+    var handler = cb.handlers_.shift();
+    this.handleNativeResult_(state, node.funcThis_, handler(state.value));
+    return;
+  }
+  if (state.catch_ && state.throw_) {
+    // Callback a 'catch' handler
+    if (queued) {
+      // Called via queued callback
+      // Just call the callback directly
+      this.handleNativeResult_(state, node.funcThis_, state.catch_(state.throw_));
+      state.catch_ = null;
+      return;
+    } else {
+      // Immediate callback from CallExpression
+      // Modify existing Callback object to execute catch steps
+      cb.stateless_ = true; // Callback can only use its handler for return value
+      cb.handlers_ = [state.catch_];
+      cb.value = state.throw_; // Set stateless value to pass to handler
+      cb.force_ = true; // Force callback to run again
+    }
+  }
+  stack.pop();
+  if (this.stateStack.length === 1) {
+    // Save value as return value if we were the last to be executed
+    this.value = state.value;
+  }
+};
+
 Interpreter.prototype['stepExpressionStatement'] = function(stack, state, node) {
   if (!state.done_) {
     this.value = undefined;
@@ -4536,3 +4796,6 @@ Interpreter.prototype['getGlobalScope'] = Interpreter.prototype.getGlobalScope;
 Interpreter.prototype['getStateStack'] = Interpreter.prototype.getStateStack;
 Interpreter.prototype['setStateStack'] = Interpreter.prototype.setStateStack;
 Interpreter['VALUE_IN_DESCRIPTOR'] = Interpreter.VALUE_IN_DESCRIPTOR;
+Interpreter.prototype['callFunction'] = Interpreter.prototype.callFunction;
+Interpreter.prototype['queueFunction'] = Interpreter.prototype.queueFunction;
+Interpreter.prototype['createThrowable'] = Interpreter.prototype.createThrowable;