Illustrators are hand gestures made during conversation. Following Bavelas, Hagen, Lane, and Lawrie (1989), we propose a new division of illustrators, into topic and interactive gestures. Interactive gestures refer to the interlocutor rather than to the topic of conversation, and they help maintain the conversation as a social system. They subsume but are not limited to the category previously called beats or batons. Three tests of this theory are reported here. In Experiment 1, the same narrative task was assigned to both dyads and individuals: Dyads had a higher rate of interactive gestures than did individuals, but the opposite pattern was shown for topic gestures. In Experiment 2, we manipulated visual availability: The rate of interactive gestures was higher for partners interacting face-to-face than for those who could not see each other, but topic gestures were not significantly affected by condition. Thus, in both experiments, interactive and topic gestures responded differently to social variables, which strongly suggests they are functionally distinct groups. A final analysis showed that, in both data sets, interactive gestures were less redundant with the words they accompanied than were topic gestures, which supports our hypothesis that they maintain involvement with the interlocutor without interrupting the verbal flow of discourse.