This text attempts to present the entire philosophy of Thomas Aquinas in a clear, simple, and precise manner. In nineteen systematically structured chapters, Thomistic philosophy is introduced in a modern, lively, and understandable form for those interested in philosophy and students. The author places a particular emphasis on epistemology, but also addresses metaphysics, the theory of change and causality, ethics, aesthetics, and the philosophy of science, as well as the ethics and social philosophy of Aquinas in their fundamental aspects. This work is particularly well-suited for a first overview of the foundations of Aristotelian-Thomistic philosophy.