Catholicism, as it developed in colonial Mexico, helped to create a broad and remarkably inclusive community of Christian subjects, while it also divided that community into countless smaller flocks. Taking this contradiction as a starting point, Matthew D. O'Hara describes how religious thought and practice shaped Mexico's popular politics. As he shows, religion faciliated the emergence of new categories and modes of belonging in which individuals-initially subjects of the Spanish crown, but later citizens and other residents of republican Mexico-found both significant opportunities for improving their place in society and major constraints on their ways of thinking and behaving.