Why are religious parties so popular in the new and emerging democracies of the Middle East and North Africa? This paper offers an alternative to the traditional accounts that stress religiosity, the repressive nature of the previous regimes, poverty and underdevelopment, or Arab grievances against Israel. Instead, it outlines a rational choice-based explanation, in which religious political parties are able to address the problem of credible commitment, ubiquitous in new democracies. Instead of having to rely on patronage as the only mechanism of making pre-electoral commitments, Islamic parties are able to directly make credible promises about the supply of public goods. This is because they already have a history and a reputation, which both serve as channels of communication with the voters. Their reputation relies most importantly on a track record of providing social services in environments where governments have failed to do so. Furthermore, we argue that their religious nature makes them well equipped to overcome collective action problems.