As Egypt’s largest opposition group, the Muslim Brotherhood is uniquely situated to play a leading role in this era of political transition. Although some welcome the Brotherhood’s involvement, others view its growing infl uence with apprehension and dismay. Such diff ering reactions refl ect serious disagreements about the credibility of the Brotherhood’s commitments to pluralism and democracy, as well as on whether its rising power poses a threat to regional peace and stability. At the core of such disagreements are fundamental diff erences of opinion on a number of key issues. First, what is the Brotherhood and what does it want? Second, how much support does it enjoy among members of the wider Egyptian public, and how well-positioned is it to convert that support into political power? Th ird, and perhaps most consequentially, to what extent, and in what ways, has the Brotherhood moved away from its radical anti-system past? Such questions raise the larger issue of whether “fundamentalist” religious groups are capable of self-transformation through their involvement in the give-and-take of democratic politics, a subject with broader relevance to our understanding of social movement change writ large.