This intellectual and social history is the first comprehensive biography of Pilgram Marpeck (c. 1495-1556), a radical reformer and lay leader of Anabaptist groups in Switzerland, Austria, and South Germany. Marpeck's influential life and work provide a glimpse of the theologies and practices of the Roman Church and of various reform movements in sixteenth-century Europe. Drawing on extensive archival data documenting Marpeck's professional life, as well as on his numerous published and unpublished writings on theology and religious reform, Stephen B. Boyd traces Marpeck's unconventional transition from mining magistrate to Anabaptist leader, establishes his connections with various radical social and religious groups, and articulates aspects of his social theology. Marpeck's distinctive and eclectic theology, Boyd demonstrates, focused on the need for personal, uncoerced conversion, rejected state interference in the affairs of the church, denied the need for a monastic withdrawal from the secular world, and called for the Christian's active pursuit of justice before God and among human beings.