In the free marketplace of religious ideas that is the United States, Americans have disagreed over many things. The form of church government, the proper way to worship, the extent of the scriptural canon, and the limits of racial and gender inclusion are but a few of the questions on which the nation’s majority Christians have erected boundaries among themselves, to say nothing of their differences with non-Christians. Yet an equally important source of denominational divisions has been the nexus of issues surrounding agency (humans’ freedom to act as they choose), voluntarism (defined here as the quest for salvation through this-worldly action), and predestination (the otherworldly question of whether God predetermines each person’s eternal destiny). Particularly contentious has been the question of predestination, especially the problem of whether God elects persons for salvation conditionally (based on their foreseen faith or merit) or unconditionally (based solely on his inscrutable wisdom). In the 16th and 17th centuries, this debate cut across the Reformation divide, with each position represented among both Catholic and Protestant scholastics. The New England Puritan clergy were the first major bearers of this scholastic tradition, which abounded with paradox and logical distinctions. The intensity of Puritanism’s predestinarian psychology generated a widespread anti-Calvinist backlash in the 19th century and contributed to the growth of a number of upstart denominations, including Methodists, Universalists, Restoration Movement “Christians,” Mormons, Adventists, and Christian Scientists. Debates over free will and predestination also bred factionalism and even threatened schism in several denominations, including the Congregationalists, Lutherans, Presbyterians, and Baptists. Less frequently, non-Christians weighed in, occasionally embracing the trope of anti-Calvinism as a way to demonstrate their own traditions’ compatibility with American freedom. By the early 21st century, though the rise of nondenominational megachurches and an increase in “nones” (people with no religious identification) had weakened the hold of traditional doctrines on many Americans, the tension between voluntarism and predestination remained basic to theism as it has been for millennia.