diff --git a/modules/graphics/src/main/java/com/sun/javafx/application/PlatformImpl.java b/modules/graphics/src/main/java/com/sun/javafx/application/PlatformImpl.java
--- a/modules/graphics/src/main/java/com/sun/javafx/application/PlatformImpl.java
+++ b/modules/graphics/src/main/java/com/sun/javafx/application/PlatformImpl.java
@@ -133,7 +133,8 @@
     /**
      * This method is invoked typically on the main thread. At this point,
      * the JavaFX Application Thread has not been started. Any attempt
-     * to call startup twice results in an exception.
+     * to call startup more than once results in all subsequent calls turning into
+     * nothing more than a runLater call with the provided Runnable being called.
      * @param r
      */
     public static void startup(final Runnable r) {
diff --git a/modules/graphics/src/main/java/javafx/application/Platform.java b/modules/graphics/src/main/java/javafx/application/Platform.java
--- a/modules/graphics/src/main/java/javafx/application/Platform.java
+++ b/modules/graphics/src/main/java/javafx/application/Platform.java
@@ -40,6 +40,53 @@
     }
 
     /**
+     * This method starts the JavaFX runtime. In general it is not necessary to
+     * explicitly call this method (it is generally invoked as a consequence of
+     * how most JavaFX applications are built), however there are valid use cases
+     * for calling this method directly. Because this method starts the JavaFX
+     * runtime, there is not yet any JavaFX Application Thread, so it is normal
+     * that this method is called directly on the main thread of the application.
+     *
+     * <p>As noted, it is normally the case that the JavaFX Application Thread
+     * is started automatically. It is important that this method only be called
+     * when the JavaFX runtime has not yet been initialized. Situations where
+     * the JavaFX runtime is started automatically include:
+     *
+     * <ul>
+     *   <li>Standard JavaFX applications that extend {@see Application}, and
+     *   use either the Java launcher or one of the launch methods in the
+     *   Application class to launch the application, the FX runtime is
+     *   initialized automatically by the launcher before the Application
+     *   class is loaded.</li>
+     *   <li>For Swing applications that use JFXPanel to display FX content, the
+     *   FX runtime is initialized when the first JFXPanel instance is
+     *   constructed.</li>
+     *   <li>For SWT application that use FXCanvas to display FX content, the FX
+     *   runtime is initialized when the first FXCanvas instance is
+     *   constructed.</li>
+     * </ul>
+     *
+     * <p>When an application does not follow any of these common approaches,
+     * then it becomes the responsibility of the developer to manually start the
+     * JavaFX runtime by calling this startup method.
+     *
+     * <p>Calling this method multiple times is discouraged, but will have no
+     * effect beyond placing the provided Runnable onto the event queue (in
+     * other words, it becomes equivalent to calling {@link #runLater(Runnable)}.
+     * For this reason, it is highly recommended that the startup method only
+     * be called once, with all subsequent uses instead making use of
+     * {@link #runLater(Runnable)}.
+     * </p>
+     *
+     * @param runnable the Runnable whose run method will be executed on the
+     * JavaFX Application Thread once it has been started.
+     * @since 9
+     */
+    public static void startup(Runnable runnable) {
+        PlatformImpl.startup(runnable);
+    }
+
+    /**
      * Run the specified Runnable on the JavaFX Application Thread at some
      * unspecified
      * time in the future. This method, which may be called from any thread,
@@ -72,6 +119,9 @@
      * runtime is initialized when the first JFXPanel instance is constructed.
      * For SWT application that use FXCanvas to display FX content, the FX
      * runtime is initialized when the first FXCanvas instance is constructed.
+     * For applications that do not follow any of these approaches, then it is
+     * necessary to manually start the JavaFX runtime by calling
+     * {@link #startup(Runnable)} once.
      * </p>
      *
      * @param runnable the Runnable whose run method will be executed on the