While theoretical models of conflict often treat actors as unitary, most selfdetermination groups are fragmented into a number of competing internal factions. This article presents a framework for understanding the ‘‘dual contests’’ that selfdetermination groups engage in—the first with their host state and the second between co-ethnic factions within groups. Using a new data set of the number of factions within a sample of self-determination groups from 1960 to 2008, the authors find that competition between co-ethnic factions is a key determinant of their conflict behavior. More competing factions are associated with higher instances of violence against the state as well as more factional fighting and attacks on co-ethnic civilians. More factions using violence increases the chances that other factions will do so, and the entry of a new faction prompts violence from existing factions in a within-group contest for political relevance. These findings have implications for both theory and policy.