In a subject as well established as the juristic contribution to medieval political thought the relative neglect of one of its major exponents, Baldus de Ubaldis, may cause surprise. The political thought of his teacher and colleague, Bartolus of Sassoferrato, is so well known that in the pantheon of late medieval political thinkers he ranks with Aquinas and Marsilius of Padua; and indeed no treatment of medieval political thought is complete without a consideration of his ideas. Yet Baldus who was certainly the juristic peer of Bartolus has received a scattered and piecemeal study of his political ideas rather than any systematic treatment aiming at completeness. Indeed Baldus' contribution as a whole to legal history lacks its historian. This is so despite the fact that Baldus shared with Bartolus the greatest fame and influence amongst the Commentators, the school of jurists which originating in the late thirteenth century dominated Roman law studies in the late Middle Ages, and indeed as the mos italicus (Italian manner) remained highly influential throughout the sixteenth century and beyond. Furthermore Baldus (unlike Bartolus) was also a canonist of renown. This inadequate modern treatment of Baldus' ideas means that it has so far proved impossible accurately to assess Baldus' general stature as a jurist. Since Baldus in his legal commentaries ranged over the whole gamut of those aspects of contemporary society relevant to juristic treatment, the total picture of his contribution to jurisprudence will surely emerge through specialised studies of specific aspects of his thought; and it is within this larger context that this book, being a study of his political thought in particular, should be located.