This chapter presents the theoretical arguments of the book, which come from the literatures on political opportunities and democratic transitions, in particular protracted transitions and transitions from below. The chapter first compares Mexico’s democratic transition to other democratization processes in which insurgent social movements play a crucial role, such as the cases of El Salvador and South Africa. Then it provides an analysis of the opportunities that democratic transitions may open for the mobilization, success, and survival of an insurgent social movement. Third, hypotheses contextualized to the Mexican case illustrate how these expectations may influence the development of a specific movement’s cycle of protests, negotiating success, and chances of survival within a protracted democratic transition.