Research on the political consequences of social movements has recently accelerated. We take stock of this research with a focus on movements in democratic polities and the United States in comparative and historical perspective. Although most studies demonstrate the influence of the largest movements, this research has not addressed how much movements matter. As for the conditions under which movements matter, scholars have been revising their initial hypotheses that the strategies, organizational forms, and political contexts that aid mobilization also aid in gaining and exerting political influence. Scholars are exploring alternative arguments about the productivity of different actions and characteristics of movements and movement organizations in the varied political contexts and institutional settings they face. Researchers are also employing more innovative research designs to appraise these more complex arguments. Scholarship will advance best if scholars continue to think through the interactions between strategies, organizations, and contexts; address movement influences on processes in institutional politics beyond the agenda-setting stage; situate case studies in comparative and historical perspective; and make more comparisons across movements and issues.