Few philosophers or theologians exerted as much influence on the shape of Medieval thought as Thomas Aquinas and he ranks amongst the most famous of the Western philosophers. He was responsible for almost single handedly bringing the philosophy of Aristotle into harmony with Christianity and was amongst the first philosophers to argue that philosophy and theology could support each other. The shape of metaphysics, theology and Aristotelian thought today still bears the imprint of Aquinas work. In this extensive and deeply researched study, Eleonore Stump engages Aquinas across the full range of his philosophical writings. She examines Aquinas' major works, Summa Theologiae and Summa Contra Gentiles and clearly assesses the vast range of Aquinas' thought from his metaphysics, theology, philosophy of mind and epistemology to his views on free will, action, the soul and ethics, law and politics. She considers the influence of Aquinas' thought on contemporary philosophy and why he should still be read today. Philosophers, theologians and students of the medieval period alike will find this unrivalled study an indispensable resource in researching and teaching Aquinas.