A review of the past decade’s research on American associations reveals significant growth in empirical findings across three levels of analysis: the individual member, the organization, and the political system. The social correlates of joining and participation, particularly gender and race differences, and the effect of incentives on individual decisions continued to attract the interest of many researchers. At the organization level, the structure of incentives and the impact of collective decision-making processes received less attention than the social ecology of association growth and differentiation, The advocacy explosion of recent years that brought many new groups and lobbying methods to Washington stimulated much research on associations in the pressure group system. The field of association research as a whole, however, still suffers from a lack of theoretical consensus on the central issues and of means for studying them.