Abstract: We introduce an acting-based animation system for creating and editing character animation at interactive speeds. Our system requires minimal training, typically under an hour, and is well suited for rapidly prototyping and creating expressive motion. A real-time motion-capture framework records the user's motions for simultaneous analysis and playback on a large screen. The animator's realworld, expressive motions are mapped into the character's virtual world. Visual feedback maintains a tight coupling between the animator and character. Complex motion is created by layering multiple passes of acting. We also introduce a novel motion-editing technique, which derives implicit relationships between the animator and character. The animator mimics some aspect of the character motion, and the system infers the association between features of the animator's motion and those of the character. The animator modifies the mimic by acting again, and the system maps the changes onto the character. We demonstrate our system with several examples and present the results from informal user studies with expert and novice animators.