File > Send to MotionBuilder

NoteSend to MotionBuilder is only available in the Maya File menu if you have matching versions of Maya and MotionBuilder. (Maya 2013 and MotionBuilder 2013 are matching versions.)

Send as New Scene: Opens a new scene in MotionBuilder, and sends the selected objects from Maya.

This option launches MotionBuilder if it is not already running. If already running, MotionBuilder prompts you to save the current scene or cancel. Selecting Cancel stops the send operation.
Update Current Scene: Available only if MotionBuilder is running. Updates the MotionBuilder scene by sending the current Maya selection. If no objects are selected, Maya sends any previously sent objects.
Add to Current Scene: Available only if MotionBuilder is running. Sends the current selection. Any selected objects that have already been sent are duplicated in the MotionBuilder scene.
Select Previously Sent Objects: Selects all objects previously sent to MotionBuilder.

This option is a convenient way to see which objects are already being shared, and to choose which objects to add to the selection.
Live Connection: Opens the Live Connection window. See Live character streaming.