Rebel organizations cannot be understood solely in terms of their coercive capacities. Many seek to displace the state and usurp its functions. How do rebel groups establish systems of governance? Applying Migdal’s state in society approach, I show how rebel governance can evolve through alliances with societal forces. I do so by focusing on the evolution of the Free Aceh Movement (GAM) in Indonesia. GAM came to govern a handful of districts by allying with two groups – rural Islamic teachers (ulama) and urban student activists – whose goals and identities were in many ways at odds with its own. These rebel state/society alliances were mutually beneficial. Ulama and activists gained security and were able to pursue their agendas through GAM, which in turn gained wider support and the capacity to govern the local population. These alliances were also transformative, resulting in significant convergence in terms of the identities and goals of all parties.