This study explores the structural and functional continuities between medieval monasticism and early Anabaptism. Anabaptists have traditionally been designated as the "radicals" or the "left wing" of the Reformation, with the implication that they departed even further from Rome than did the followers of Luther, Calvin and Zwingli. However, even in the 16th century, contemporaries noted that a kind of similitude existed between the Anabaptist "radicals" and their enemies in Rome. Examination of the writings of early Anabaptists on adult baptism alongside the writings of monastic authors shows that structural similarities do indeed exist between monks committed to Rome and Anabaptists who rejected infant baptism. These writings also reveal significant borrowing and transformation of medieval mystical themes and values, in particular Gelassenheit, a concept adopted from medieval German mysticism. This study argues that it is the very transformation of Gelassenheit among early Anabaptists which allowed them to create communities which came to resemble monastic communities, built around the vows taken by believers at their baptism. This communal identity formation took place in a context of nearly constant persecution, leading to martyrdom being posited as the ultimate responsibility and goal of the baptismal vow. This study focuses on three groups of texts: the writings of two influential German Anabaptist leaders: Balthasar Hubmair and Pilgram Marpeck who wrote respectively on individual and ecclesial development in the movement and a collection of hymns penned by the followers of Phillip Plener while they were imprisoned in the castle dungeon at Passau. These three groups of texts, written at different points in the Anabaptist story provide three glimpses into critical ways in which key figures in this movement utilized and transformed fundamentally medieval notions regarding baptism, martyrdom and Gelassenheit. They help to explain how those who purportedly wanted nothing to do with "monkish" things nonetheless formed communities which resembled monastic communities. In their attempt to return to the church of Christ and the apostles, the Anabaptists adopted and adapted key medieval concepts to create something innovative.