This dissertation examines the interplay of American Protestants with the doctrine of original sin in mid-twentieth-century America. In this period, lay believers--regardless of age, gender, denomination, or education--engaged the sin-centered thought of Reinhold Niebuhr, Paul Tillich, and Billy Graham. In their correspondence to each Protestant leader, believers praised, questioned, and criticized Niebuhr, Tillich, and Graham's views on the human condition. These conversations about the meaning and nature of sin also helped ordinary Protestants make sense of the harrowing events of depression, war, and cold war, and the anxieties and struggles of everyday life. By arguing that the concept of original sin, though contested and variously interpreted, was an active agent in the lives of everyday believers this project complicates the usual characterization of mid-century Protestant expression as unconcerned with theological doctrine. The argument also resists overly schematic typologies of belief--such as highbrow, middlebrow, and lowbrow--and advances the category of lay theologian to revise our understanding of postwar Protestantism. This alternative perspective not only reframes how we understand the mid-century religious landscape, but also contributes to the ongoing conversation about the nature of human nature and places current public discussion of sin and evil in a larger context.