diff --git a/common/changes/office-ui-fabric-react/yubojia-focusTrapZone_2018-12-11-22-54.json b/common/changes/office-ui-fabric-react/yubojia-focusTrapZone_2018-12-11-22-54.json
new file mode 100644
index 0000000000000..957f1fe6eb5e6
--- /dev/null
+++ b/common/changes/office-ui-fabric-react/yubojia-focusTrapZone_2018-12-11-22-54.json
@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "office-ui-fabric-react",
+      "comment": "FocusTrapZone - Make forceFocusInsideTrap prop changes modify focus",
+      "type": "patch"
+    }
+  ],
+  "packageName": "office-ui-fabric-react",
+  "email": "yubojia@microsoft.com"
+}
\ No newline at end of file
diff --git a/packages/office-ui-fabric-react/etc/office-ui-fabric-react.api.ts b/packages/office-ui-fabric-react/etc/office-ui-fabric-react.api.ts
index 60497cbe18258..22900502f032b 100644
--- a/packages/office-ui-fabric-react/etc/office-ui-fabric-react.api.ts
+++ b/packages/office-ui-fabric-react/etc/office-ui-fabric-react.api.ts
@@ -1294,7 +1294,7 @@ class FocusTrapZone extends BaseComponent<IFocusTrapZoneProps, {}>, implements I
   // (undocumented)
   componentDidMount(): void;
   // (undocumented)
-  componentWillMount(): void;
+  componentDidUpdate(prevProps: IFocusTrapZoneProps): void;
   // (undocumented)
   componentWillReceiveProps(nextProps: IFocusTrapZoneProps): void;
   // (undocumented)
diff --git a/packages/office-ui-fabric-react/src/components/FocusTrapZone/FocusTrapZone.tsx b/packages/office-ui-fabric-react/src/components/FocusTrapZone/FocusTrapZone.tsx
index b41470dfa7ba3..03d380bf1f8bc 100644
--- a/packages/office-ui-fabric-react/src/components/FocusTrapZone/FocusTrapZone.tsx
+++ b/packages/office-ui-fabric-react/src/components/FocusTrapZone/FocusTrapZone.tsx
@@ -21,20 +21,8 @@ export class FocusTrapZone extends BaseComponent<IFocusTrapZoneProps, {}> implem
   private _hasFocusHandler: boolean;
   private _hasClickHandler: boolean;
 
-  public componentWillMount(): void {
-    FocusTrapZone._focusStack.push(this);
-  }
-
   public componentDidMount(): void {
-    const { elementToFocusOnDismiss, disableFirstFocus = false } = this.props;
-
-    this._previouslyFocusedElementOutsideTrapZone = elementToFocusOnDismiss
-      ? elementToFocusOnDismiss
-      : (document.activeElement as HTMLElement);
-    if (!elementContains(this._root.current, this._previouslyFocusedElementOutsideTrapZone) && !disableFirstFocus) {
-      this.focus();
-    }
-
+    this._bringFocusIntoZone();
     this._updateEventHandlers(this.props);
   }
 
@@ -47,25 +35,24 @@ export class FocusTrapZone extends BaseComponent<IFocusTrapZoneProps, {}> implem
     this._updateEventHandlers(nextProps);
   }
 
-  public componentWillUnmount(): void {
-    const { ignoreExternalFocusing } = this.props;
-
-    this._events.dispose();
-    FocusTrapZone._focusStack = FocusTrapZone._focusStack.filter((value: FocusTrapZone) => {
-      return this !== value;
-    });
+  public componentDidUpdate(prevProps: IFocusTrapZoneProps) {
+    const prevForceFocusInsideTrap = prevProps.forceFocusInsideTrap !== undefined ? prevProps.forceFocusInsideTrap : true;
+    const newForceFocusInsideTrap = this.props.forceFocusInsideTrap !== undefined ? this.props.forceFocusInsideTrap : true;
 
-    const activeElement = document.activeElement as HTMLElement;
-    if (
-      !ignoreExternalFocusing &&
-      this._previouslyFocusedElementOutsideTrapZone &&
-      typeof this._previouslyFocusedElementOutsideTrapZone.focus === 'function' &&
-      (elementContains(this._root.current, activeElement) || activeElement === document.body)
-    ) {
-      focusAsync(this._previouslyFocusedElementOutsideTrapZone);
+    if (!prevForceFocusInsideTrap && newForceFocusInsideTrap) {
+      // Transition from forceFocusInsideTrap disabled to enabled. Emulate what happens when a FocusTrapZone gets mounted
+      this._bringFocusIntoZone();
+    } else if (prevForceFocusInsideTrap && !newForceFocusInsideTrap) {
+      // Transition from forceFocusInsideTrap enabled to disabled. Emulate what happens when a FocusTrapZone gets unmounted
+      this._returnFocusToInitiator();
     }
   }
 
+  public componentWillUnmount(): void {
+    this._events.dispose();
+    this._returnFocusToInitiator();
+  }
+
   public render(): JSX.Element {
     const { className, ariaLabelledBy } = this.props;
     const divProps = getNativeProps(this.props, divProperties);
@@ -114,6 +101,37 @@ export class FocusTrapZone extends BaseComponent<IFocusTrapZoneProps, {}> implem
     }
   }
 
+  private _bringFocusIntoZone(): void {
+    const { elementToFocusOnDismiss, disableFirstFocus = false } = this.props;
+
+    FocusTrapZone._focusStack.push(this);
+
+    this._previouslyFocusedElementOutsideTrapZone = elementToFocusOnDismiss
+      ? elementToFocusOnDismiss
+      : (document.activeElement as HTMLElement);
+    if (!elementContains(this._root.current, this._previouslyFocusedElementOutsideTrapZone) && !disableFirstFocus) {
+      this.focus();
+    }
+  }
+
+  private _returnFocusToInitiator(): void {
+    const { ignoreExternalFocusing } = this.props;
+
+    FocusTrapZone._focusStack = FocusTrapZone._focusStack.filter((value: FocusTrapZone) => {
+      return this !== value;
+    });
+
+    const activeElement = document.activeElement as HTMLElement;
+    if (
+      !ignoreExternalFocusing &&
+      this._previouslyFocusedElementOutsideTrapZone &&
+      typeof this._previouslyFocusedElementOutsideTrapZone.focus === 'function' &&
+      (elementContains(this._root.current, activeElement) || activeElement === document.body)
+    ) {
+      focusAsync(this._previouslyFocusedElementOutsideTrapZone);
+    }
+  }
+
   private _updateEventHandlers(newProps: IFocusTrapZoneProps): void {
     const { isClickableOutsideFocusTrap = false, forceFocusInsideTrap = true } = newProps;
 
diff --git a/packages/office-ui-fabric-react/src/components/Panel/Panel.types.ts b/packages/office-ui-fabric-react/src/components/Panel/Panel.types.ts
index 3cf215d62fe92..764acea35d985 100644
--- a/packages/office-ui-fabric-react/src/components/Panel/Panel.types.ts
+++ b/packages/office-ui-fabric-react/src/components/Panel/Panel.types.ts
@@ -129,9 +129,9 @@ export interface IPanelProps extends React.HTMLAttributes<PanelBase> {
   ignoreExternalFocusing?: boolean;
 
   /**
-   * Indicates whether Panel should force focus inside the focus trap zone
+   * Indicates whether Panel should force focus inside the focus trap zone.
+   * If not explicitly specified, behavior aligns with FocusTrapZone's default behavior.
    * Deprecated, use `focusTrapZoneProps`.
-   * @defaultvalue true
    * @deprecated Use `focusTrapZoneProps`.
    */
   forceFocusInsideTrap?: boolean;