How does the resource base of a rebel group impact its membership, structure, and behavior? While scholars, analysts, and policy makers increasingly link natural resources to the onset and duration of civil war, this article explores how resource endowments shape the character and conduct of rebel groups. This article identifies a rebel "resource curse" much like the one that undermines state institutions in resource-rich environments. While the presence of economic endowments makes it possible for leaders to recruit on the basis of short-term rewards, these groups are flooded with opportunistic joiners who exhibit little commitment to the long-term goals of the organization. In resource-poor environments, leaders attract new recruits by drawing on social ties to make credible promises about the private rewards that will come with victory. Opportunistic joiners stay away from these movements, leaving a pool of activist recruits willing to invest their time and energy in the hope of reaping large gains in the future.