The study aims to explore how Islamist parties mobilize citizens in electoral authoritarian systems. Specifically, I analyze how Islamist parties develop identity, outreach, structure, and linkages to wide sections of the population, so that when the political opportunity presents itself, people are informed of their existence, goals, and representatives, and hence, primed to vote for them. The study adopts and expands the Political Process Theory, and adapts it to address North Africa, a region in which such theoretical scholarship has until now not been conducted. Indepth case studies focus on two Islamist parties in North Africa — Tunisia’s Ennahda and Algeria’s HMS, which both adopted the Muslim Brotherhood model, had charismatic leaders, and were both active on the political scene from 1989-2014, the period between their first electoral trial and their electoral participation after taking part in governance. On the supply side, this study’s main focus, are the key dimensions concerning the mobilizers — Islamist parties: their capacity to accumulate resources, and their approaches to ensure Islamic discourse is part of the political process. I analyze how these two elements interact with each other at those times when political opportunity is made available by those in government, whether through division among elites or in attempts to play party blocs off each other. The demand side looks at the parties’ political appeal to citizen sensibilities through various Islamist agendas. By presenting Islamic discourse as a means to gather large numbers to their cause, the parties seek to show themselves capable of incorporating popular views into their agendas, and thus to give voters alternatives when the opportunity presents itself for them to vote against the government. I contend that in North African political contexts characterized by electoral authoritarian or resilient authoritarian systems, demand is largely guided by cautious party calculation of benefits and costs. Benefits represent a rejection of the regime and the potential to change the status quo (through economic improvement, citizen engagement); costs involve the potential loss of citizen rights and of social stability. The cases of Ennahda and Hamas/Harakat Mujtami’a al-Silm (HMS) reveal that in responding to the constraints of electoral authoritarianism, which include controlled inclusion and informal tolerance as well as outright repression, the parties demonstrated efficiency in supplying Islamic debate, political locations of Islamic activism, and an alternative discourse to that of the regime. However, in doing so, they often failed to meet specific voter demands or expectations, or even to garner a protest vote. The study suggests that mobilizing Islamic politics served to engage the population and make the political realm culturally credible. Yet, the costs were very high, affecting the parties’ organizational strength, credibility, and capacity to create cooperative alliances, and even their ability to retain political control over the use of Islamic discourse.