Petrus Baldus De Ubaldis (1327-1406), Italian jurist, a member of the noble family of the Ubaldi (Baldeschi), was born at Perugia in 1327, and studied civil law there under Bartolus, being admitted to the degree of doctor of civil law at the early age of seventeen. Federicus Petrucius of Siena is said to have been the master under whom he studied canon law. Upon his promotion to the doctorate he at once proceeded to Bologna, where he taught law for three years; after which he was advanced to a professorship at Perugia, where he remained for thirty-three years. He taught law subsequently at Pisa, at Florence, at Padua and at Pavia, at a time when the schools of law in those universities disputed the palm with the school of Bologna. He died at Pavia on the 28th of April 1406. The extant works of Baldus hardly bear out the great reputation which he acquired amongst his contemporaries, due partly to the active part he took in public affairs, and partly to the fame he acquired by his consultations, of which five volumes have been published (Frankfort, 1589). Baldus was the master of Pierre Roger de Beaufort, who became pope under the title of Gregory XI., and whose immediate successor, Urban VI., summoned Baldus to Rome to assist him by his consultations in 1380 against the anti-pope Clement VII. Cardinal de Zabarella and Paulus Castrensis were also amongst his pupils.

His Commentary on the Liber Feudorum, is considered to be one of the best of his works, which were unfortunately left by him for the most part in an incomplete state. His brothers Angelus (1328-1407) and Petrus (1335-1400) were of almost equal eminence with himself as jurists.