In philosophy, besides commentaries on almost all the works of Aristotle, he wrote several special treatises. But his main work is the treatise "De regimine principum," written for, and dedicated to, his pupil, Philip IV. It passed through many editions (the first, Augsburg, 1473) and was translated into several languages. The Roman edition of 1607 contains a life of Egidio. The work is divided into three books: the first treats of the individual conduct of the king, the nature of his true happiness, the choice and acquisition of virtues, and the ruling of passions; the second deals with family life and the relations with wife, children, and servants; the third considers the State, its origin, and the proper mode of governing in times of peace and war.