We introduce "directed improvisation," a new paradigm for human-computer interaction (HCI). Users direct computer "characters" with abstract instructions and constraints. The characters improvise behaviors that follow the directions, express their personal styles, and meet other objectives. We illustrate directed improvisation with our current testbed application, a Computer-Animated Improvisational Theater for children, and discuss its properties as an HCI paradigm. KEYWORDS : Interaction Paradigm, Intelligent systems, Educational applications, Entertainment applications. 1. INTRODUCTION To improvise is to invent, create, or perform a new work in real time, without detailed preparation and often by making use of the resources at hand. Improvisation may be constrained by self-imposed or exogenously supplied directions. The resulting "new work" realizes a prescribed structure in an inventive form. The most striking examples of "directed improvisation" occur in the theater [8, 10, 22,...