Since the end of the Cold War religion has increasingly become an organized subject and object of American foreign policy. This has been notable with the emergence of four religious foreign policy regimes—International Religious Freedom, Faith-Based Foreign Aid, Muslim and Islamic Interventions, and Religious Engagement—which together constitute an American foreign policy regime complex on religion. The introduction poses the book’s three guiding questions. First, why and how did these different, yet closely related, religious foreign policy regimes emerge? Second, have the boundaries between religion and state been redefined by these regimes, and if so, how? Third, what are the global effects of the growing entanglement between faith and American foreign policy? The chapter introduces the concepts and arguments that are central to answering these questions. It also highlights the contributions made to the existing literature, discusses some definitional and methodological issues, and presents the plan of the book.