diff --git a/common/changes/office-ui-fabric-react/master_2018-02-12-21-15.json b/common/changes/office-ui-fabric-react/master_2018-02-12-21-15.json
new file mode 100644
index 00000000000000..760c8144a8dac3
--- /dev/null
+++ b/common/changes/office-ui-fabric-react/master_2018-02-12-21-15.json
@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "office-ui-fabric-react",
+      "comment": "Fix aria-owns in contextual menu items, and add appropriate aria properties to CommandBar items.",
+      "type": "patch"
+    }
+  ],
+  "packageName": "office-ui-fabric-react",
+  "email": "trgau@microsoft.com"
+}
\ No newline at end of file
diff --git a/packages/office-ui-fabric-react/src/components/CommandBar/CommandBar.test.tsx b/packages/office-ui-fabric-react/src/components/CommandBar/CommandBar.test.tsx
index ac810998684d0c..5626722982de89 100644
--- a/packages/office-ui-fabric-react/src/components/CommandBar/CommandBar.test.tsx
+++ b/packages/office-ui-fabric-react/src/components/CommandBar/CommandBar.test.tsx
@@ -43,6 +43,52 @@ describe('CommandBar', () => {
     expect(tree).toMatchSnapshot();
   });
 
+  it('adds the correct aria-setsize and -posinset attributes to the command bar items.', () => {
+    const items: IContextualMenuItem[] = [
+      {
+        name: 'TestText 1',
+        key: 'TestKey1',
+        className: 'item1',
+        subMenuProps: {
+          items: [
+            {
+              name: 'SubmenuText 1',
+              key: 'SubmenuKey1',
+              className: 'SubMenuClass'
+            }
+          ]
+        }
+      },
+      {
+        name: 'TestText 2',
+        key: 'TestKey2',
+        className: 'item2',
+      },
+      {
+        name: 'TestText 3',
+        key: 'TestKey3',
+        className: 'item3',
+      },
+    ];
+
+    const renderedContent = ReactTestUtils.renderIntoDocument<CommandBar>(
+      <CommandBar
+        items={ items }
+      />
+    ) as React.Component<CommandBar, {}>;
+    document.body.appendChild(ReactDOM.findDOMNode(renderedContent));
+
+    console.log(document.body.innerHTML);
+
+    const [item1, item2, item3] = ['.item1', '.item2', '.item3'].map(i => document.querySelector(i)!.children[0]);
+    expect(item1.getAttribute('aria-setsize')).toBe('3');
+    expect(item2.getAttribute('aria-setsize')).toBe('3');
+    expect(item3.getAttribute('aria-setsize')).toBe('3');
+    expect(item1.getAttribute('aria-posinset')).toBe('1');
+    expect(item2.getAttribute('aria-posinset')).toBe('2');
+    expect(item3.getAttribute('aria-posinset')).toBe('3');
+  });
+
   it('opens a menu with deprecated IContextualMenuItem.items property', () => {
     const items: IContextualMenuItem[] = [
       {
diff --git a/packages/office-ui-fabric-react/src/components/CommandBar/CommandBar.tsx b/packages/office-ui-fabric-react/src/components/CommandBar/CommandBar.tsx
index a40a2bb30501ea..380c19195a352c 100644
--- a/packages/office-ui-fabric-react/src/components/CommandBar/CommandBar.tsx
+++ b/packages/office-ui-fabric-react/src/components/CommandBar/CommandBar.tsx
@@ -110,14 +110,17 @@ export class CommandBar extends BaseComponent<ICommandBarProps, ICommandBarState
         </div>
       );
     }
+    // Total # of menu items is regular items + far items + 1 for the ellipsis, if necessary
+    const setSize = renderedItems!.length + renderedFarItems!.length + (renderedOverflowItems && renderedOverflowItems.length > 0 ? 1 : 0);
+    let posInSet = 1;
 
     return (
       <div className={ css('ms-CommandBar', styles.root, className) } ref='commandBarRegion'>
         { searchBox }
         <FocusZone ref='focusZone' className={ styles.container } direction={ FocusZoneDirection.horizontal } role='menubar' >
           <div className={ css('ms-CommandBar-primaryCommands', styles.primaryCommands) } ref='commandSurface'>
-            { renderedItems!.map((item, index) => (
-              this._renderItemInCommandBar(item, index, expandedMenuItemKey!)
+            { renderedItems!.map(item => (
+              this._renderItemInCommandBar(item, posInSet++, setSize, expandedMenuItemKey!)
             )).concat((renderedOverflowItems && renderedOverflowItems.length) ? [
               <div className={ css('ms-CommandBarItem', styles.item) } key={ OVERFLOW_KEY } ref={ OVERFLOW_KEY }>
                 <button
@@ -131,6 +134,8 @@ export class CommandBar extends BaseComponent<ICommandBarProps, ICommandBarState
                   aria-expanded={ this.state.expandedMenuItemKey === OVERFLOW_KEY }
                   aria-label={ this.props.elipisisAriaLabel || '' }
                   aria-haspopup={ true }
+                  aria-setsize={ setSize }
+                  aria-posinset={ posInSet++ }
                   data-automation-id='commandBarOverflow'
                 >
                   <Icon className={ css('ms-CommandBarItem-overflow', styles.itemOverflow) } iconName='more' />
@@ -139,8 +144,8 @@ export class CommandBar extends BaseComponent<ICommandBarProps, ICommandBarState
             ] : []) }
           </div>
           <div className={ css('ms-CommandBar-sideCommands', styles.sideCommands) } ref='farCommandSurface'>
-            { renderedFarItems!.map((item, index) => (
-              this._renderItemInCommandBar(item, index, expandedMenuItemKey!, true)
+            { renderedFarItems!.map(item => (
+              this._renderItemInCommandBar(item, posInSet++, setSize, expandedMenuItemKey!, true)
             )) }
           </div>
         </FocusZone>
@@ -163,7 +168,7 @@ export class CommandBar extends BaseComponent<ICommandBarProps, ICommandBarState
     this.refs.focusZone.focus();
   }
 
-  private _renderItemInCommandBar(item: ICommandBarItemProps, index: number, expandedMenuItemKey: string, isFarItem?: boolean) {
+  private _renderItemInCommandBar(item: ICommandBarItemProps, posInSet: number, setSize: number, expandedMenuItemKey: string, isFarItem?: boolean) {
     if (item.onRender) {
       return (
         <div className={ css('ms-CommandBarItem', styles.item, item.className) } key={ item.key } ref={ item.key }>
@@ -172,7 +177,7 @@ export class CommandBar extends BaseComponent<ICommandBarProps, ICommandBarState
       );
     }
 
-    const itemKey = item.key || String(index);
+    const itemKey = item.key || String(posInSet);
     const isLink = item.onClick || hasSubmenu(item);
     const className = css(
       isLink ? ('ms-CommandBarItem-link ' + styles.itemLink) : ('ms-CommandBarItem-text ' + styles.itemText),
@@ -196,6 +201,8 @@ export class CommandBar extends BaseComponent<ICommandBarProps, ICommandBarState
           aria-expanded={ hasSubmenu(item) ? expandedMenuItemKey === item.key : undefined }
           role='menuitem'
           aria-label={ ariaLabel }
+          aria-setsize={ setSize }
+          aria-posinset={ posInSet }
         >
           { (hasIcon) ? this._renderIcon(item) : (null) }
           { isNameVisible && (
@@ -222,6 +229,8 @@ export class CommandBar extends BaseComponent<ICommandBarProps, ICommandBarState
           aria-haspopup={ hasSubmenu(item) }
           role='menuitem'
           aria-label={ ariaLabel }
+          aria-setsize={ setSize }
+          aria-posinset={ posInSet }
         >
           { (hasIcon) ? this._renderIcon(item) : (null) }
           { isNameVisible && (
@@ -243,6 +252,8 @@ export class CommandBar extends BaseComponent<ICommandBarProps, ICommandBarState
           data-command-key={ itemKey }
           aria-haspopup={ hasSubmenu(item) }
           aria-label={ ariaLabel }
+          aria-setsize={ setSize }
+          aria-posinset={ posInSet }
         >
           { (hasIcon) ? this._renderIcon(item) : (null) }
           { (isNameVisible) && (
diff --git a/packages/office-ui-fabric-react/src/components/CommandBar/__snapshots__/CommandBar.test.tsx.snap b/packages/office-ui-fabric-react/src/components/CommandBar/__snapshots__/CommandBar.test.tsx.snap
index 06410c197e976b..1d75d3b33a5d1a 100644
--- a/packages/office-ui-fabric-react/src/components/CommandBar/__snapshots__/CommandBar.test.tsx.snap
+++ b/packages/office-ui-fabric-react/src/components/CommandBar/__snapshots__/CommandBar.test.tsx.snap
@@ -24,6 +24,8 @@ exports[`CommandBar renders CommandBar correctly 1`] = `
           aria-expanded={false}
           aria-haspopup={true}
           aria-label={undefined}
+          aria-posinset={1}
+          aria-setsize={1}
           className="ms-CommandBarItem-link undefined"
           data-command-key="TestKey1"
           id="CommandBar0TestKey1"
diff --git a/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.test.tsx b/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.test.tsx
index 628199910bb4e9..be5b2f4147d9d5 100644
--- a/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.test.tsx
+++ b/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.test.tsx
@@ -179,6 +179,39 @@ describe('ContextualMenu', () => {
     expect(document.querySelector('.SubMenuClass')).toBeDefined();
   });
 
+  it('sets the correct aria-owns attribute for the submenu', () => {
+    const submenuId = 'testSubmenuId';
+    const items: IContextualMenuItem[] = [
+      {
+        name: 'TestText 1',
+        key: 'TestKey1',
+        subMenuProps: {
+          id: submenuId,
+          items: [
+            {
+              name: 'SubmenuText 1',
+              key: 'SubmenuKey1',
+              className: 'SubMenuClass'
+            }
+          ]
+        }
+      },
+    ];
+
+    ReactTestUtils.renderIntoDocument<ContextualMenu>(
+      <ContextualMenu
+        items={ items }
+      />
+    );
+
+    const parentMenuItem = document.querySelector('button.ms-ContextualMenu-link') as HTMLButtonElement;
+    ReactTestUtils.Simulate.click(parentMenuItem);
+    const childMenu = document.getElementById(submenuId);
+
+    expect(childMenu!.id).toBe(submenuId);
+    expect(parentMenuItem.getAttribute('aria-owns')).toBe(submenuId);
+  });
+
   it('still works with deprecated IContextualMenuItem.items property', () => {
     const items: IContextualMenuItem[] = [
       {
diff --git a/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.tsx b/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.tsx
index a1457b818c0946..ce5d86bcf794d2 100644
--- a/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.tsx
+++ b/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.tsx
@@ -492,6 +492,10 @@ export class ContextualMenu extends BaseComponent<IContextualMenuProps, IContext
     hasCheckmarks?: boolean,
     hasIcons?: boolean) {
     let { expandedMenuItemKey, subMenuId } = this.state;
+    if (item.subMenuProps && item.subMenuProps.id) {
+      subMenuId = item.subMenuProps.id;
+    }
+
     let ariaLabel = '';
 
     if (item.ariaLabel) {
@@ -503,11 +507,12 @@ export class ContextualMenu extends BaseComponent<IContextualMenuProps, IContext
     const isChecked: boolean | null | undefined = getIsChecked(item);
     const canCheck: boolean = isChecked !== null;
     const defaultRole = canCheck ? 'menuitemcheckbox' : 'menuitem';
+    const itemHasSubmenu = hasSubmenu(item);
 
     const itemButtonProperties = {
       className: classNames.root,
       onClick: this._onItemClick.bind(this, item),
-      onKeyDown: hasSubmenu(item) ? this._onItemKeyDown.bind(this, item) : null,
+      onKeyDown: itemHasSubmenu ? this._onItemKeyDown.bind(this, item) : null,
       onMouseEnter: this._onItemMouseEnter.bind(this, item),
       onMouseLeave: this._onMouseItemLeave.bind(this, item),
       onMouseDown: (ev: any) => this._onItemMouseDown(item, ev),
@@ -516,9 +521,9 @@ export class ContextualMenu extends BaseComponent<IContextualMenuProps, IContext
       href: item.href,
       title: item.title,
       'aria-label': ariaLabel,
-      'aria-haspopup': hasSubmenu(item) || null,
+      'aria-haspopup': itemHasSubmenu || null,
       'aria-owns': item.key === expandedMenuItemKey ? subMenuId : null,
-      'aria-expanded': hasSubmenu(item) ? item.key === expandedMenuItemKey : null,
+      'aria-expanded': itemHasSubmenu ? item.key === expandedMenuItemKey : null,
       'aria-checked': isChecked,
       'aria-posinset': focusableElementIndex + 1,
       'aria-setsize': totalItemCount,