This book sets out a thematic presentation of human action, especially as it relates to morality, in the three most significant figures in Medieval Scholastic thought: Thomas Aquinas, John Duns Scotus, and William of Ockham. Thomas, along with his teacher Albert the Great, was instrumental in the medieval reception of the action theory of Aristotle's Nicomachean Ethics. Scotus and Ockham were part of a later Franciscan theological tradition. Thomas, Scotus, and Ockham worked in the context of a new moral theology that focused on the description and evaluation of human acts. Organised thematically, discussing the causes of human action, the role of practical reasoning, the stages of action, the specification of moral action, and an act's supernatural and natural worth, each chapter compares the three main figures on the same set of issues.The book shows that although the different philosophies of action cannot be explained in terms of any one major difference or principle, there are some common themes that deserve attention. The most notable themes are a developing separation between nature and the will; an increased emphasis on the will's activity, and a changing view of mental causation. The book is important for those who are interested in medieval philosophy, the philosophy of action, and the intellectual background to Reformation and early modern thought.