The first major study of the early Reformation and the Polish monarchy for over a century, this volume asks why Crown and church in the reign of King Sigismund I (1506-1548) did not persecute Lutherans. It offers a new narrative of Luther's dramatic impact on this monarchy - which saw violent urban Reformations and the creation of Christendom's first Lutheran principality by 1525 - placing these events in their comparative European context. King Sigismund's realm appears to offer a major example of sixteenth-century religious toleration: the king tacitly allowed his Hanseatic ports to enact local Reformations, enjoyed excellent relations with his Lutheran vassal duke in Prussia, allied with pro-Luther princes across Europe, and declined to enforce his own heresy edicts. Polish church courts allowed dozens of suspected Lutherans to walk free.