This paper examines how oppositional groups go about exploiting opportunities to mobilize en masse in settings that are less than auspicious. The Green Movement is used here as a case study, the aim of which is to show that understanding how a people go about mobilizing requires, first and foremost, examining the core beliefs that motivate them to seize opportunities when conditions allow. To this end, a constructivist approach will be used to demonstrate that it was the oppositional forces that took a proactive role in constructing opportunities to mobilize because they perceived the circumstances to be favorable, which suggests that greater attention ought to be focused on the sociopolitical and historical context within which a given situation is viewed as conducive to mass mobilization. Citing the examples of the student and women’s groups involved in Iran’s Green Movement, and tracing their historical trajectories and particular experiences during Ahmadinejad’s first term (2004–2008), I argue that the Green Movement may be best described as a ‘movement of movements,’ the kind of mega social movement capable of harnessing the potential, not only of Iranians but of other Middle East peoples, to mobilize with a view to pursuing specific social and political goals. This approach has the virtue of offering a way to understand specific traits of social movements operating in repressive settings.