diff --git a/specs/Modal.spec.js b/specs/Modal.spec.js
index c801fff3..c4a61dda 100644
--- a/specs/Modal.spec.js
+++ b/specs/Modal.spec.js
@@ -11,11 +11,18 @@ import sinon from 'sinon';
 import expect from 'expect';
 import ReactDOM from 'react-dom';
 import Modal from '../src/components/Modal';
-import * as ariaAppHider from '../src/helpers/ariaAppHider';
 import { renderModal, unmountModal, emptyDOM } from './helper';
 
 const Simulate = TestUtils.Simulate;
 
+function getDefaultProps () {
+  return {
+    getAppElement () {},
+    contentLabel: 'Test Modal',
+    isOpen: true
+  };
+}
+
 
 describe('Modal', () => {
   afterEach('check if test cleaned up rendered modals', emptyDOM);
@@ -24,38 +31,28 @@ describe('Modal', () => {
   it('focuses the last focused element when tabbing in from browser chrome');
 
   it('can be open initially', () => {
-    const component = renderModal({ isOpen: true }, 'hello');
+    const component = renderModal(getDefaultProps(), 'hello');
     expect(component.portal.content.innerHTML.trim()).toEqual('hello');
   });
 
   it('can be closed initially', () => {
-    const component = renderModal({}, 'hello');
+    const props = {
+      ...getDefaultProps(),
+      isOpen: false
+    };
+    const component = renderModal(props, 'hello');
     expect(ReactDOM.findDOMNode(component.portal).innerHTML.trim()).toEqual('');
   });
 
-  it('accepts appElement as a prop', () => {
-    const el = document.createElement('div');
-    const node = document.createElement('div');
-    ReactDOM.render(
-      <Modal
-        isOpen
-        appElement={el}
-      />
-    , node);
-    expect(el.getAttribute('aria-hidden')).toEqual('true');
-    ReactDOM.unmountComponentAtNode(node);
-  });
-
   it('renders into the body, not in context', () => {
     const node = document.createElement('div');
     const App = () => (
       <div>
-        <Modal isOpen>
+        <Modal {...getDefaultProps()} getAppElement={() => node}>
           hello
         </Modal>
       </div>
     );
-    Modal.setAppElement(node);
     ReactDOM.render(<App />, node);
     const modalParent = document.body.querySelector('.ReactModalPortal').parentNode;
     expect(modalParent).toEqual(document.body);
@@ -64,69 +61,62 @@ describe('Modal', () => {
 
   it('renders children', () => {
     const child = 'I am a child of Modal, and he has sent me here...';
-    const component = renderModal({ isOpen: true }, child);
+    const component = renderModal(getDefaultProps(), child);
     expect(component.portal.content.innerHTML).toEqual(child);
   });
 
   it('renders the modal content with a dialog aria role when provided ', () => {
     const child = 'I am a child of Modal, and he has sent me here...';
-    const component = renderModal({ isOpen: true, role: 'dialog' }, child);
+    const component = renderModal({ ...getDefaultProps(), role: 'dialog' }, child);
     expect(component.portal.content.getAttribute('role')).toEqual('dialog');
   });
 
   it('renders the modal with a aria-label based on the contentLabel prop', () => {
     const child = 'I am a child of Modal, and he has sent me here...';
-    const component = renderModal({ isOpen: true, contentLabel: 'Special Modal' }, child);
-    expect(component.portal.content.getAttribute('aria-label')).toEqual('Special Modal');
+    const component = renderModal(getDefaultProps(), child);
+    expect(component.portal.content.getAttribute('aria-label')).toEqual('Test Modal');
   });
 
   it('has default props', () => {
+    const testProps = getDefaultProps();
     const node = document.createElement('div');
-    Modal.setAppElement(document.createElement('div'));
-    const component = ReactDOM.render(<Modal />, node);
+    testProps.getAppElement = () => document.createElement('div');
+    const component = ReactDOM.render(<Modal {...testProps} />, node);
     const props = component.props;
-    expect(props.isOpen).toBe(false);
     expect(props.ariaHideApp).toBe(true);
     expect(props.closeTimeoutMS).toBe(0);
     expect(props.shouldCloseOnOverlayClick).toBe(true);
     ReactDOM.unmountComponentAtNode(node);
-    ariaAppHider.resetForTesting();
-    Modal.setAppElement(document.body);  // restore default
   });
 
   it('removes the portal node', () => {
-    const component = renderModal({ isOpen: true }, 'hello');
+    const component = renderModal(getDefaultProps(), 'hello');
     expect(component.portal.content.innerHTML.trim()).toEqual('hello');
     unmountModal();
     expect(!document.querySelector('.ReactModalPortal')).toExist();
   });
 
   it('focuses the modal content', () => {
-    renderModal({ isOpen: true }, null, function checkModalContentFocus () {
+    renderModal(getDefaultProps(), null, function checkModalContentFocus () {
       expect(document.activeElement).toEqual(this.portal.content);
     });
   });
 
   it('give back focus to previous element or modal.', (done) => {
-    const modal = renderModal({
-      isOpen: true,
-      onRequestClose () {
-        done();
-      }
-    }, null, () => {});
-
-    renderModal({
-      isOpen: true,
-      onRequestClose () {
-        Simulate.keyDown(modal.portal.content, {
-          // The keyCode is all that matters, so this works
-          key: 'FakeKeyToTestLater',
-          keyCode: 27,
-          which: 27
-        });
-        expect(document.activeElement).toEqual(modal.portal.content);
-      }
-    }, null, function checkPortalFocus () {
+    const testProps = getDefaultProps();
+    testProps.onRequestClose = () => done();
+    const modal = renderModal(testProps, null, () => {});
+    const testProps2 = getDefaultProps();
+    testProps2.onRequestClose = () => {
+      Simulate.keyDown(modal.portal.content, {
+        // The keyCode is all that matters, so this works
+        key: 'FakeKeyToTestLater',
+        keyCode: 27,
+        which: 27
+      });
+      expect(document.activeElement).toEqual(modal.portal.content);
+    };
+    renderModal(testProps2, null, function checkPortalFocus () {
       expect(document.activeElement).toEqual(this.portal.content);
       Simulate.keyDown(this.portal.content, {
         // The keyCode is all that matters, so this works
@@ -145,13 +135,13 @@ describe('Modal', () => {
       />
     );
 
-    renderModal({ isOpen: true }, input, () => {
+    renderModal(getDefaultProps(), input, () => {
       expect(document.activeElement).toEqual(document.querySelector('.focus_input'));
     });
   });
 
   it('handles case when child has no tabbable elements', () => {
-    const component = renderModal({ isOpen: true }, 'hello');
+    const component = renderModal(getDefaultProps(), 'hello');
     expect(() => {
       Simulate.keyDown(component.portal.content, { key: 'Tab', keyCode: 9, which: 9 });
     }).toNotThrow();
@@ -159,7 +149,7 @@ describe('Modal', () => {
 
   it('keeps focus inside the modal when child has no tabbable elements', () => {
     let tabPrevented = false;
-    const modal = renderModal({ isOpen: true }, 'hello');
+    const modal = renderModal(getDefaultProps(), 'hello');
     expect(document.activeElement).toEqual(modal.portal.content);
     Simulate.keyDown(modal.portal.content, {
       key: 'Tab',
@@ -171,47 +161,47 @@ describe('Modal', () => {
   });
 
   it('supports portalClassName', () => {
-    const modal = renderModal({ isOpen: true, portalClassName: 'myPortalClass' });
+    const modal = renderModal({ ...getDefaultProps(), portalClassName: 'myPortalClass' });
     expect(modal.node.className).toEqual('myPortalClass');
   });
 
   it('supports custom className', () => {
-    const modal = renderModal({ isOpen: true, className: 'myClass' });
+    const modal = renderModal({ ...getDefaultProps(), className: 'myClass' });
     expect(modal.portal.content.className.indexOf('myClass')).toNotEqual(-1);
   });
 
   it('supports overlayClassName', () => {
-    const modal = renderModal({ isOpen: true, overlayClassName: 'myOverlayClass' });
+    const modal = renderModal({ ...getDefaultProps(), overlayClassName: 'myOverlayClass' });
     expect(modal.portal.overlay.className.indexOf('myOverlayClass')).toNotEqual(-1);
   });
 
   it('overrides the default styles when a custom classname is used', () => {
-    const modal = renderModal({ isOpen: true, className: 'myClass' });
+    const modal = renderModal({ ...getDefaultProps(), className: 'myClass' });
     expect(modal.portal.content.style.top).toEqual('');
   });
 
   it('overrides the default styles when a custom overlayClassName is used', () => {
-    const modal = renderModal({ isOpen: true, overlayClassName: 'myOverlayClass' });
+    const modal = renderModal({ ...getDefaultProps(), overlayClassName: 'myOverlayClass' });
     expect(modal.portal.overlay.style.backgroundColor).toEqual('');
   });
 
   it('supports adding style to the modal contents', () => {
-    const modal = renderModal({ isOpen: true, style: { content: { width: '20px' } } });
+    const modal = renderModal({ ...getDefaultProps(), style: { content: { width: '20px' } } });
     expect(modal.portal.content.style.width).toEqual('20px');
   });
 
   it('supports overriding style on the modal contents', () => {
-    const modal = renderModal({ isOpen: true, style: { content: { position: 'static' } } });
+    const modal = renderModal({ ...getDefaultProps(), style: { content: { position: 'static' } } });
     expect(modal.portal.content.style.position).toEqual('static');
   });
 
   it('supports adding style on the modal overlay', () => {
-    const modal = renderModal({ isOpen: true, style: { overlay: { width: '75px' } } });
+    const modal = renderModal({ ...getDefaultProps(), style: { overlay: { width: '75px' } } });
     expect(modal.portal.overlay.style.width).toEqual('75px');
   });
 
   it('supports overriding style on the modal overlay', () => {
-    const modal = renderModal({ isOpen: true, style: { overlay: { position: 'static' } } });
+    const modal = renderModal({ ...getDefaultProps(), style: { overlay: { position: 'static' } } });
     expect(modal.portal.overlay.style.position).toEqual('static');
   });
 
@@ -220,45 +210,46 @@ describe('Modal', () => {
     // Just in case the default style is already relative, check that we can change it
     const newStyle = previousStyle === 'relative' ? 'static' : 'relative';
     Modal.defaultStyles.content.position = newStyle;
-    const modal = renderModal({ isOpen: true });
+    const modal = renderModal(getDefaultProps());
     expect(modal.portal.content.style.position).toEqual(newStyle);
     Modal.defaultStyles.content.position = previousStyle;
   });
 
   it('adds class to body when open', () => {
-    renderModal({ isOpen: false });
+    const testProps = { ...getDefaultProps(), isOpen: false };
+    renderModal(testProps);
     expect(document.body.className.indexOf('ReactModal__Body--open') !== -1).toEqual(false);
     unmountModal();
 
-    renderModal({ isOpen: true });
+    renderModal(getDefaultProps());
     expect(document.body.className.indexOf('ReactModal__Body--open') !== -1).toEqual(true);
     unmountModal();
 
-    renderModal({ isOpen: false });
+    renderModal(testProps);
     expect(document.body.className.indexOf('ReactModal__Body--open') !== -1).toEqual(false);
   });
 
   it('removes class from body when unmounted without closing', () => {
-    renderModal({ isOpen: true });
+    renderModal(getDefaultProps());
     expect(document.body.className.indexOf('ReactModal__Body--open') !== -1).toEqual(true);
     unmountModal();
     expect(document.body.className.indexOf('ReactModal__Body--open') !== -1).toEqual(false);
   });
 
-  it('removes aria-hidden from appElement when unmounted without closing', () => {
+  it('sets aria-hidden to false on appElement when unmounted without closing', () => {
     const el = document.createElement('div');
     const node = document.createElement('div');
     ReactDOM.render(React.createElement(Modal, {
-      isOpen: true,
-      appElement: el
+      ...getDefaultProps(),
+      getAppElement () { return el; }
     }), node);
     expect(el.getAttribute('aria-hidden')).toEqual('true');
     ReactDOM.unmountComponentAtNode(node);
-    expect(el.getAttribute('aria-hidden')).toEqual(null);
+    expect(el.getAttribute('aria-hidden')).toEqual('false');
   });
 
   it('adds --after-open for animations', () => {
-    renderModal({ isOpen: true });
+    renderModal(getDefaultProps());
     const overlay = document.querySelector('.ReactModal__Overlay');
     const content = document.querySelector('.ReactModal__Content');
     expect(overlay.className.match(/ReactModal__Overlay--after-open/)).toExist();
@@ -268,7 +259,7 @@ describe('Modal', () => {
   it('should trigger the onAfterOpen callback', () => {
     const afterOpenCallback = sinon.spy();
     renderModal({
-      isOpen: true,
+      ...getDefaultProps(),
       onAfterOpen: afterOpenCallback
     });
     expect(afterOpenCallback.called).toBeTruthy();
@@ -276,7 +267,7 @@ describe('Modal', () => {
 
   it('check the state of the modal after close with time out and reopen it', () => {
     const modal = renderModal({
-      isOpen: true,
+      ...getDefaultProps(),
       closeTimeoutMS: 2000,
       onRequestClose () {}
     });
@@ -289,7 +280,7 @@ describe('Modal', () => {
   it('should close on Esc key event', () => {
     const requestCloseCallback = sinon.spy();
     const modal = renderModal({
-      isOpen: true,
+      ...getDefaultProps(),
       shouldCloseOnOverlayClick: true,
       onRequestClose: requestCloseCallback
     });
@@ -310,6 +301,75 @@ describe('Modal', () => {
     expect(event.key).toEqual('FakeKeyToTestLater');
   });
 
+  describe('Show/Hide appElement', () => {
+    let elementArray;
+    let node;
+    beforeEach(() => {
+      const el = document.createElement('div');
+      const el2 = document.createElement('div');
+      const el3 = document.createElement('div');
+      elementArray = [el, el2, el3];
+      node = document.createElement('div');
+    });
+
+    it('hides an array of appElements', () => {
+      ReactDOM.render(
+        <Modal
+          {...getDefaultProps()}
+          getAppElement={() => elementArray}
+        />
+      , node);
+      const values = elementArray.map(ae => ae.getAttribute('aria-hidden'));
+      expect(values).toEqual(['true', 'true', 'true']);
+      ReactDOM.unmountComponentAtNode(node);
+    });
+
+    it('shows an array of appElements', () => {
+      ReactDOM.render(
+        <Modal
+          {...getDefaultProps()}
+          getAppElement={() => elementArray}
+        />
+      , node);
+      ReactDOM.unmountComponentAtNode(node);
+      const values = elementArray.map(ae => ae.getAttribute('aria-hidden'));
+      expect(values).toEqual(['false', 'false', 'false']);
+    });
+
+    it('hides a single appElement', () => {
+      ReactDOM.render(
+        <Modal
+          {...getDefaultProps()}
+          getAppElement={() => elementArray[0]}
+        />
+      , node);
+      expect(elementArray[0].getAttribute('aria-hidden')).toEqual('true');
+      ReactDOM.unmountComponentAtNode(node);
+    });
+
+    it('shows a single appElement', () => {
+      ReactDOM.render(
+        <Modal
+          {...getDefaultProps()}
+          getAppElement={() => elementArray[0]}
+        />
+      , node);
+      ReactDOM.unmountComponentAtNode(node);
+      expect(elementArray[0].getAttribute('aria-hidden')).toEqual('false');
+    });
+
+    it('throws an error if appElement is not provided', () => {
+      function renderError () {
+        ReactDOM.render(
+          <Modal
+            {...getDefaultProps()}
+          />
+        , node);
+      }
+      expect(renderError).toThrow('react-modal: Setting an getAppElement function is required');
+    });
+  });
+
   describe('should close on overlay click', () => {
     afterEach('Unmount modal', emptyDOM);
 
@@ -317,12 +377,12 @@ describe('Modal', () => {
       afterEach('Unmount modal', emptyDOM);
 
       it('verify default prop of shouldCloseOnOverlayClick', () => {
-        const modal = renderModal({ isOpen: true });
+        const modal = renderModal(getDefaultProps());
         expect(modal.props.shouldCloseOnOverlayClick).toEqual(true);
       });
 
       it('verify prop of shouldCloseOnOverlayClick', () => {
-        const modal = renderModal({ isOpen: true, shouldCloseOnOverlayClick: false });
+        const modal = renderModal({ ...getDefaultProps(), shouldCloseOnOverlayClick: false });
         expect(modal.props.shouldCloseOnOverlayClick).toEqual(false);
       });
     });
@@ -333,7 +393,7 @@ describe('Modal', () => {
       it('verify overlay click when shouldCloseOnOverlayClick sets to false', () => {
         const requestCloseCallback = sinon.spy();
         const modal = renderModal({
-          isOpen: true,
+          ...getDefaultProps(),
           shouldCloseOnOverlayClick: false
         });
         expect(modal.props.isOpen).toEqual(true);
@@ -346,7 +406,7 @@ describe('Modal', () => {
       it('verify overlay click when shouldCloseOnOverlayClick sets to true', () => {
         const requestCloseCallback = sinon.spy();
         const modal = renderModal({
-          isOpen: true,
+          ...getDefaultProps(),
           shouldCloseOnOverlayClick: true,
           onRequestClose () {
             requestCloseCallback();
@@ -362,7 +422,7 @@ describe('Modal', () => {
       it('verify overlay mouse down and content mouse up when shouldCloseOnOverlayClick sets to true', () => {
         const requestCloseCallback = sinon.spy();
         const modal = renderModal({
-          isOpen: true,
+          ...getDefaultProps(),
           shouldCloseOnOverlayClick: true,
           onRequestClose: requestCloseCallback
         });
@@ -379,7 +439,7 @@ describe('Modal', () => {
       it('verify content mouse down and overlay mouse up when shouldCloseOnOverlayClick sets to true', () => {
         const requestCloseCallback = sinon.spy();
         const modal = renderModal({
-          isOpen: true,
+          ...getDefaultProps(),
           shouldCloseOnOverlayClick: true,
           onRequestClose () {
             requestCloseCallback();
@@ -398,7 +458,7 @@ describe('Modal', () => {
       it('should not stop event propagation', () => {
         let hasPropagated = false;
         const modal = renderModal({
-          isOpen: true,
+          ...getDefaultProps(),
           shouldCloseOnOverlayClick: true
         });
         const overlay = TestUtils.scryRenderedDOMComponentsWithClass(modal.portal, 'ReactModal__Overlay');
@@ -419,7 +479,7 @@ describe('Modal', () => {
     it('verify event passing on overlay click', () => {
       const requestCloseCallback = sinon.spy();
       const modal = renderModal({
-        isOpen: true,
+        ...getDefaultProps(),
         shouldCloseOnOverlayClick: true,
         onRequestClose: requestCloseCallback
       });
@@ -443,7 +503,7 @@ describe('Modal', () => {
   it('adds --before-close for animations', () => {
     const closeTimeoutMS = 50;
     const modal = renderModal({
-      isOpen: true,
+      ...getDefaultProps(),
       closeTimeoutMS
     });
 
@@ -463,7 +523,7 @@ describe('Modal', () => {
     const closeTimeoutMS = 50;
 
     renderModal({
-      isOpen: true,
+      ...getDefaultProps(),
       closeTimeoutMS
     });
 
diff --git a/src/components/Modal.js b/src/components/Modal.js
index 2089f81e..59abe32d 100644
--- a/src/components/Modal.js
+++ b/src/components/Modal.js
@@ -1,13 +1,11 @@
 import React, { Component } from 'react';
 import ReactDOM from 'react-dom';
-import ExecutionEnvironment from 'exenv';
 import elementClass from 'element-class';
 import ModalPortal from './ModalPortal';
 import * as ariaAppHider from '../helpers/ariaAppHider';
 
 const renderSubtreeIntoContainer = ReactDOM.unstable_renderSubtreeIntoContainer;
 
-const SafeHTMLElement = ExecutionEnvironment.canUseDOM ? window.HTMLElement : {};
 
 function getParentElement (parentSelector) {
   return parentSelector();
@@ -23,7 +21,12 @@ export default class Modal extends Component {
       overlay: React.PropTypes.object
     }),
     portalClassName: React.PropTypes.string,
-    appElement: React.PropTypes.instanceOf(SafeHTMLElement),
+    /**
+     * A function that returns the appElement that will be aria-hidden
+     * when the modal is open. The function should return a DOMElement or
+     * an array of DOMElements.
+     */
+    getAppElement: React.PropTypes.func.isRequired,
     onAfterOpen: React.PropTypes.func,
     onRequestClose: React.PropTypes.func,
     closeTimeoutMS: React.PropTypes.number,
@@ -69,10 +72,6 @@ export default class Modal extends Component {
     }
   };
 
-  static setAppElement (element) {
-    ariaAppHider.setElement(element);
-  }
-
   static injectCSS () {
     return process.env.NODE_ENV !== 'production'
         && console.warn('React-Modal: injectCSS has been deprecated ' +
@@ -102,7 +101,7 @@ export default class Modal extends Component {
 
   componentWillUnmount () {
     if (this.props.ariaHideApp) {
-      ariaAppHider.show(this.props.appElement);
+      ariaAppHider.show(this.props.getAppElement());
     }
 
     const state = this.portal.state;
@@ -137,7 +136,7 @@ export default class Modal extends Component {
     }
 
     if (props.ariaHideApp) {
-      ariaAppHider.toggle(props.isOpen, props.appElement);
+      ariaAppHider.toggle(this.props.getAppElement(), props.isOpen);
     }
 
     this.portal = renderSubtreeIntoContainer(this,
diff --git a/src/helpers/ariaAppHider.js b/src/helpers/ariaAppHider.js
index f5ee72e9..aa4b83fe 100644
--- a/src/helpers/ariaAppHider.js
+++ b/src/helpers/ariaAppHider.js
@@ -1,37 +1,24 @@
-let globalElement = typeof document !== 'undefined' ? document.body : null;
-
 function validateElement (appElement) {
-  if (!appElement && !globalElement) {
-    throw new Error('react-modal: You must set an element with `Modal.setAppElement(el)` to make this accessible');
+  if (!appElement) {
+    throw new Error('react-modal: Setting an getAppElement function is required');
   }
 }
 
-export function setElement (element) {
-  let newElement = element;
-  if (typeof newElement === 'string') {
-    const el = document.querySelectorAll(element);
-    newElement = 'length' in el ? el[0] : el;
+export function toggle (appElement, value) {
+  validateElement(appElement);
+  if (Array.isArray(appElement)) {
+    appElement.forEach((ae) => {
+      ae.setAttribute('aria-hidden', value);
+    });
+  } else {
+    appElement.setAttribute('aria-hidden', value);
   }
-  globalElement = newElement || globalElement;
-  return globalElement;
 }
 
 export function hide (appElement) {
-  validateElement(appElement);
-  (appElement || globalElement).setAttribute('aria-hidden', 'true');
+  toggle(appElement, true);
 }
 
 export function show (appElement) {
-  validateElement(appElement);
-  (appElement || globalElement).removeAttribute('aria-hidden');
-}
-
-export function toggle (shouldHide, appElement) {
-  if (shouldHide) {
-    hide(appElement);
-  } else { show(appElement); }
-}
-
-export function resetForTesting () {
-  globalElement = document.body;
+  toggle(appElement, false);
 }