In this final edition of his classic study of St. Thomas Aquinas, Etienne Gilson presents the sweeping range and organic unity of Thomistic philosophical thought. Gilson demonstrates that Aquinas drew from a wide spectrum of sources in the development of his thought from Aristotle to the Arabic and Jewish philosophers of his time, as well as from Christian writers. What results is an insightful introduction to the thought of Aquinas and the Scholastic philosophy of the Middle Ages.