This dissertation is a social and cultural history of the Adult Bible Class Movement. It is the first scholarly work to uncover this heretofore unknown devotional revolution that swept through American Protestantism at the turn of the twentieth century. In focusing on this Bible study movement I uncover individuals and institutions overlooked by scholars, analyze understudied evangelical practices of Bible study, and challenge prevailing historical interpretations on the relationship between evangelicalism and politics in America. Bible classes, I argue, were lay innovations meant to curb an exodus of young people from the church beginning in the late nineteenth century. Through Biblical devotions and civic engagement, they became the site where the twentieth century’s first generation of evangelicals navigated the era’s sweeping social and cultural transformations. Claiming at its peak over five million members in nearly fifty thousand classes, the Adult Bible Class Movement became the grassroots base of the Prohibition and Anti-Evolution crusades of the 1920s. By focusing on the devotional lives, religious practices, and cultural worldviews of the lay women and men who served as Bible class teachers, students and advocates, I argue that the Adult Bible Class Movement was the crucible from which modern America’s evangelical subculture emerged.