This book features a unified presentation of the theory of quarks and gluons. Included are perturbative aspects, such as deep inelastic scattering, jets, Drell-Yan scattering, and exclusive processes, and nonperturbative aspects, such as current algebra and PCAC techniques, and instantons, together with an introduction to lattice QCD. Additional topics, for example, QCD sum rules and the quark model of hadrons, are also to be found. The emphasis is on detailed calculations and results that can be tested against experiment. The aim is to bring readers to the point where they can start to work on their own, as well as to give a comprehensive idea of the quality of the theory. Some of the subjects are presented for the first time in book form; indeed a few are totally new. Among these are a full discussion of relativistic and nonperturbative corrections to heavy quark bound states, the interpretation of K factors, and some aspects of jet physics. The book is ideally suited as a textbook for graduate students in nuclear and particle physics, but owing to the many recent results it will also be appreciated by researchers in these fields.