Chapter 2 introduces and validates the authors’ measurement of their main theoretical concept, American religious exceptionalism. It provides a detailed portrayal of who adheres to American religious exceptionalism, the “disciples,” by juxtaposing their various religious identities, beliefs, and behaviors to American religious exceptionalism’s “dissidents,” and those who are more neutral in their adherence, the “laity.” The uniqueness of American piety vis-à-vis other industrialized nations’ religious beliefs, behaviors, and commitments is quite apparent. The authors explicate how Americans view their relationship between God and nation as uniquely American. Shifting toward an analysis of the disciples, this chapter uncovers several social, ideological, demographic characteristics that differentiate the disciples from the dissidents and the laity. Drawing on an impressive array of global and national survey data, the chapter provides strong empirical support for American religious exceptionalism as a distinct concept from other measures.