In much of the Muslim world, Islamic political and economic movements appear to have a comparative advantage. Relative to similar secular groups, they are better able to mobilize supporters and sustain their cooperation long-term. Nowhere is this more apparent than in Turkey, a historically secular country that has experienced a sharp rise in Islamic-based political and economic activity. Drawing on rich data sources and econometric methods, Avital Livny challenges existing explanations - such as personal faith - for the success of these movements. Instead, Livny shows that the Islamic advantage is rooted in feelings of trust among individuals with a shared, religious group-identity. This group-based trust serves as an effective substitute for more generalized feelings of interpersonal trust, which are largely absent in many Muslim-plurality countries. The book presents a new argument for conceptualizing religion as both a personal belief system and collective identity.