In the past decades scholars in the field of Thomistic studies repeatedly expressed the desirability of an up-to-date manual on the philosophy of nature and anthropology of St. Thomas Aquinas. Questions demanding to be discussed concern, for instance, the precise nature of a philosophical and a scientific approach, the place of classical philosophy of nature in our time, the value of the atomic representation of material reality, the relevance of the concept of substance. Is it still possible to speak of the human soul? What is the relation between man and the world? The author, a well-known specialist in Thomistic studies, tries to answer these and similar questions in the light of the principles of Aquinas. The explanations are placed in a historical context; the numerous notes give the relevant texts of Aquinas in Latin. Some 500 authors are quoted.