The Defender of the Peace of Marsilius of Padua is a massively influential text in the history of western political thought. Marsilius offers a detailed analysis and explanation of human political communities, before going on to attack what he sees as the obstacles to peaceful human coexistence - principally the contemporary papacy. Annabel Brett's authoritative rendition of the Defensor Pacis is the first new translation in English for fifty years, and a major contribution to the series of Cambridge Texts: all of the usual series features are provided, included chronology, notes for further reading, and up-to-date annotation aimed at the student reader encountering this classic of medieval thought for the first time. This new edition of The Defender of the Peace is a scholarly and a pedagogic event of great importance, of interest to historians, political theorists, theologians and philosophers at all levels from second-year undergraduate upwards.