It is now just over three decades since the initiation of the research and writing that came to be called resource mobilization theory (RMT). Developed during a period of heightened activism and social movement participation, it grew out of our sense that the then extant theories and approaches did not well explain the levels of mobilization and the trends that were occurring in an affluent American society. One line of those earlier theories focused on the role of grievances and deprivation in triggering social movements. But should not the level of grievances and deprivation and consequently the number of social movements be going down as society becomes more affluent? Nor did others of the available theories do very well at explaining the large number of movements and high level of mobilization of the period.Beginning as an attempt to provide a set of answers to that seeming paradox, we developed a fairly general but partial theory of social movement growth and decline and the relationship of growth and decline to movement structure and differentiation. The intellectual roots of RMT lie in our own background in the then current organizational and economic theories that critiqued simple notions of rationality and made it clear that self-interest alone was an inadequate basis to account for the contribution of effort to the pursuit of the collective goods that social movements seemed to be involved in. The theory took an entrepreneurialorganizational approach to movements and generated a set of topics, propositions, and hypotheses that had been little investigated in prior research and certainly had not been organized in that way before. Although the theory was stated in fairly general terms, as if it could be applied to most societies, especially industrialized societies, it was in fact designed to focus on the dynamics and trends of social movements in contemporary American society. Stated another way, the scope conditions were not well articulated.We thank Pat Gillham, Debra Minkoff, and Jackie Smith for providing useful comments on earlier drafts. RMT developed as one among several related attempts to understand collective action and social movements that shared problematics and broke with earlier traditions. Anthony Oberschall, Charles Tilly, William Gamson, Pam Oliver, Gerald Marwell, and others, though differing with each other in important ways, also shared some common assumptions. They differed, for instance, in how much they focused on the conditions for individual mobilization and participation, the extent to which they took an organizational or political process approach, how much they focused on the Olsonian problem of the provision of collective goods, and so on. As is evidenced in the essays in Zald and McCarthy (1979), the results of a conference held in 1977, on the one hand, there already was an awareness that a new paradigm or approach (which came to be called the resource mobilization/collective action program) was developing, and on the other there were substantial differences within the pro...