This thesis explores the contemporary Islamist project-constituted by those that mobilize to restructure public life according to Islamic norms-in the context of the 2011-2013 "Arab Spring".The thesis has two interrelated aims. First, it aims to empirically explore changing interactions between Islamist mobilization in politic and in society,and examine the position state in stitutions have within these changes. Second, it aims to apply insights of studies on social movements and contentious mobilization in the analysis of these interactions. The thesis'main contentions are, first,that in their practice Islamist movements face a dilemma in how to react to a context that is ever more strictly divided between a social and political arena:either mobilization is aimed at societal change through organizing as social associations, or it is aimed at maximizing political influence through organizing as political parties. Irrespective of what their ideology is, all movements face the dilemma of how to reconcile a vision of a complete Islamic system with day-to-day realities. Second, I argue that common strategies addressing the perceived "secularity" of state bureaucracies and public institutions can be the basis of a shared goal for mobilization and thereby ensure the unity of the Islamist project. Two specific debates on contentious mobilization-relating to dilemmas of strategic action and the social process of "upward scale shift"-are then used in conjuncture with one another to provide insights into how these state institutions can influence the relation between Islamist mobilization in society and politics. I substantiate these claims through a paired comparison between Syria and Tunisia. The comparison builds on, first, extensive fieldwork over the course of four years in the Arab world (mainly Syria, Tunisia, Turkey and Jordan) in whic haround 180 individuals have been interviewed. Second, it draws on a content analysis of primary sources from Islamist associations, state institutions, and individual autobiographies of (Islamist)actors; third, it uses secondary sources from local, Arab and international newspapers as the empirical basis for the analysis.