Abstract
Although a considerable amount of research on modern self-help/mutual aid has been undertaken during the past several decades, studies have yet to address the question What are the organizational dynamics underlying the institutionalization of self-help/mutual aid? As a partial answer to this question, the author describes the central patterns of growth, decline, and persistence of national self-help/mutual-aid organizations, their formal diversification, and the extent to which subpopulations gain market share. In addition to using an organizational—ecological focus to map the trajectory of voluntary organizations, this article builds on resource partitioning theory by applying its central insights to subtypes of organizations. Expansion of self-help/mutual aid is remarkably similar to the trajectories of commercial and bureaucratic populations, but expectations that generalist concentration fosters growth of specialist organizations are not supported. Specialists dominate generalists except among medical self-help/ mutual aid. Implications for future research are discussed.