This dissertation examines the Liber consolationis phisonomie by Pietro d'Abano (c. 1250-1316) and places the work both in the context of medieval psychological theories and of scholastic culture. Physiognomy, the practice of studying a person's physical appearance in order to discern his or her emotions, personality, moral character, and intellectual capacities, rests on the assumption that the physical body is somehow connected to the spiritual self. This study explores how medieval people conceived of that relationship through a broader examination of theories about emotion, personality, and intelligence. Pietro d'Abano was an unusual figure who bridged the occupational identities of physician and philosopher, just as the study of psychology bridged the disciplines of medicine and philosophy. Pietro was highly materialist in his conception of human nature. While scholars of Pietro's work have noticed this tendency in his more mature thought, especially his medical text the Conciliator, his Liber consolationis phisonomie, his earliest known work, has been largely overlooked. This is understandable, as it is largely an aphoristic summary of what physical traits indicate what mental ones. However, it provides valuable insights into the development of Pietro's thought as well as the role of physiognomy in medieval learned and popular culture. This study concludes with an examination of Pietro's legacy, namely the reputation he obtained in the Renaissance for being a magician. It examines medieval theories about magic, the role of spurious attributions in creating textual authority, and how Pietro's own materialist conception of the universe and human nature may have contributed to his constructed posthumous identity.