This article evaluates the emergence and growth of the Muslim Brotherhood in Egypt from the 1930's through the 1950's. It begins by outlining and empirically examining possible explanations for the organization's growth based on (1) theories of political Islam and (2) the concept of political opportunity structure in social movement theory. An extension of these approaches is suggested based on data from organizational documents and declassified U.S. State Department files from this period. The successful mobilization of the Muslim Brotherhood was possible because of the way its Islamic message was tied to its organizational structure, activities, and strategies and the everyday lives of Egyptians. The analysis suggests that ideas are integrated into social movements in more ways than the concept of framing allows for. It also broadens our understanding of how organizations can arise in highly repressive environments.