measures on the ballot? Stone's rich empirical description of the organizations she studies provides a strong example for other scholars that take up these new questions.

I review the development of the political opportunity or political process perspective, which has animated a great deal of research on social movements. The essential insight—that the context in which a movement emerges influences its development and potential impact—provides a fruitful analytic orientation for addressing numerous questions about social movements. Reviewing the development of the literature, however, I note that conceptualizations of political opportunity vary greatly, and scholars disagree on basic theories of how political opportunities affect movements. The relatively small number of studies testing political opportunity hypotheses against other explanations have generated mixed results, owing in part to the articulation of the theory and the specifications of variables employed. I examine conflicting specifications of the theory by considering the range of outcomes scholars address. By disaggregating outcomes and actors, I argue, we can reconcile some of the apparent contradictions and build a more comprehensive and robust theory of opportunities and social movements.

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