Historians of American religion generally agree that religious debates over slavery were characterized by a reliance on the plain meaning of the Bible. According to the conventional wisdom, antebellum Americans were uninterested in or even overtly hostile to tradition and church history. However, a close study of pro- and antislavery literature complicates this picture of ahistorical biblicism. For some defenders of slavery, not merely the Bible but also Christian tradition supported their position, and these Catholics, Episcopalians, Presbyterians, Methodists, and Baptists mined the past for examples of Christian slaveholding. On the other hand, both white and Black antislavery authors used religious history to bolster their cases against the peculiar institution, with African Americans leading the way in developing an antislavery account of the Christian past. The previously unnoticed historical dimensions of religious arguments over slavery prove central to understanding why these debates failed, while also modifying how we conceive of scripture, tradition, and religious authority in nineteenth-century America. Arguments over slavery show that religious Americans—even many who claimed to be biblicists—did not read the Bible alone but always alongside and in relation to other texts, traditions, and interpreters.