This article reviews central problems in political opportunity theory and explores the implications of adopting certain conceptualizations of political opportunities for explaining the emergence, development, and influence of protest movements. Results from multivariate analyses of civil rights protest, organizational formation, and policy outcomes indicate significant variation depending on (1) whether the political opportunity structure is conceptualized broadly or narrowly, (2) the dependent variable concerned, and (3) the underlying assumptions about the mechanisms through which opportunities translate into action. We argue that the variation in results can best be understood by adopting a broader understanding of protest and the political process and that theory development requires more careful and more explicit — although not necessarily more uniform — conceptualization and specification of political opportunity variables and models.