Research on cognitive systems adopts the aims and assumptions of classical AI research, emphasizing the construction of intelligent agents that exhibit complex behavior. This article reviews the cognitive systems paradigm and two widely adopted hypotheses—physical symbol systems and heuristic search—that underpin it. The author introduces a third claim—the social cognition hypothesis—that states intelligence requires the ability to represent and reason about others’ mental states. The article also examines a number of computational artifacts, both historical and recent, that focus on interaction and exhibit this capacity. Examples include dialogue systems, synthetic experts, believable agents, intelligent tutors, interactive robots, and instructable game players. In closing, the author identifies issues in social cognition that deserve greater attention and poses challenges that can drive future research on interactive cognitive systems.