Abstract: An animation system provides synchronization services to synchronize actions of two more interactive user interface characters that are displayed simultaneously. The animation services allow applications to make animation requests to control the actions of characters on the display. These actions include playing one of the character's animation sequences and generating speech output with lip-synched animation of the character's mouth. Accessible via script commands or an Application Programming Interface, the synchronization services allow an application to control interaction between two or more characters on the display. Applications can synchronize actions by invoking straightforward commands such as Wait, Interrupt, or Stop. In response to these commands, the animation server synchronizes scheduled actions by halting playback of a character until a specified action of another character completes or halting a specified action of one character after scheduled actions for another character are completed.