Over recent decades, Islamism—the belief that Islam should guide social and political as well as personal life—has become a powerful force throughout much of the Muslim world. Through a discussion of the Egyptian case, this essay shows how the rise of Islamism can be illuminated by findings of the literatures on revolution and civil society, and vice versa. As many leading theories on revolutions would predict, the necessary precondition for Islamism's rise has been the declining efficacy and legitimacy of the state. Yet what has occurred in Egypt (and other parts of the Arab world) is not a successful revolution but a peculiar stalemate in which the existing regime retains political power while ceding substantial control over the societal and cultural spheres to the revolutionary challenger—an outcome that the literature does not envision. This stalemate, in turn, is largely a consequence of Islamists' ability to expand their presence in civil society. This expansion in Egypt and other Arab countries over recent decades is thus best understood as a sign not of benign liberalization, but rather of profound political failure, and as an incubator for illiberal radicalism.