Resource mobilization theory has recently presented an alternative interpretation of social movements. The review traces the emergence and recent controversies generated by this new perspective. A multifactored model of social movement formation is advanced, emphasizing resources, organization, and political opportunities in addition to traditional discontent hypotheses. The McCarthy-Zald (1973) theory of entrepreneurial mobilization is critically assessed as an interpretation of the social movements of the 1960s-1970s, and the relevance of the Olson (1968) theory of collective action is specified. Group organization is argued to be the major determinant of mobilization potential and patterns. The debate between the Gerlach-Hine (1970) and entrepreneurial theories of social movement organization is traced in terms of historical changes in the social movement sector and the persistence of organizational diversity. A model of social movement politics is outlined, building on Gamson’s (1975) theory of strategy and Tilly’s (1978) polity theory by emphasizing political alliances and processes shaping success and failure. Piven & Cloward (1977) are correct that disruptiveness leads to success and that disruptions can be mobilized without formal organization; they are wrong in asserting that formal organization is necessarily incompatible with mobilization. The future development of resource mobilization theory lies in two directions: extending the polity theory to deal with different states and regimes, including the development of neo-corporatism, and providing a more sophisticated social psychology of mobilization.