Multi-participant online activities are described. In one or more implementations, a protocol is described which ties an online activity (e.g., an online game) to an instant messaging infrastructure. For example, an online game may leverage the instant messaging infrastructure to form rosters of participants for participation in the online game, Once the roster is formed, the instant messaging infrastructure may further manage the presence of the participants in the online activity, such as which users join and cease participation in the online activity and notify other users of these changes. Further, the state of participation in the online activity may be stored such that the users may continue between sessions.