Scholarship on religion in the early American republic is often shaped by two historical narratives. One is the story of the efflorescence of religion—its power, pervasiveness, and plurality. The second is the account of secularization. Once seen as the waning of religion’s power with the advent of modernity, secularization has recently been reimagined and recast by scholars in several disciplines. But to explore some themes at the intersection of recent religious histories of the early republic and neo-secularization theory is no easy task because of the instability and ambiguity of the very terms at the center of discussion: the religious and the secular. This essay reviews recent studies of the Enlightenment, the Revolution, and disestablishment and shows how they employ the categories of the religious and the secular in strikingly different ways. Seeing how these authors construct (or assume) these categories brings their works into a more productive conversation.