A system for the creation of real-time, behavior-based animated actors. The system provides tools to create actors that respond to users and to each other in real-time, with personalities and moods consistent with the author's goals and intentions. The system includes two subsystems. The first subsystem is an Animation Engine that uses procedural techniques to enable authors to create layered, continuous, non-repetitive motions and smooth transitions between them. The second subsystem is a Behavior Engine that enables authors to create sophisticated rules governing how actors communicate, change, and make decisions. The combined system provides an integrated set of tools for authoring the “minds” and “bodies” of interactive actors. The system uses an english-style scripting language so that creative experts who are not primarily programmers can create powerful interactive applications. The system allows authors of various abilities to create remarkably lifelike, responsively animated character interactions that can be run over networks in real time.