This invaluable book is an extensive set of lecture notes on various aspects of non-perturbative quantum chromodynamics - the fundamental theory of strong interaction on which nuclear and hadronic physics is based. The original edition of the book, written in the mid-1980s, had more of a review style. In the second edition the outline remains the same, but the text has been completely rewritten, and extended. Apart from the new developments over the years, this edition has benefited from several graduate courses which the author has taught at Stony Brook during the last decade. The text is now complemented by exercises and has a total of about 1000 references to major works, arranged by subject. Three major issues - the structure of the QCD vacuum, the structure of hadrons, and the physics of hot/dense matter - are addressed as physics problems. Therefore, when discussing any specific subject, the book attempts to incorporate (1) all the solid theoretical results, (2) experimental information, and (3) results of numerical (lattice) simulations, which are playing an increasing role in quantum field theory in general, and the development of QCD in particular. "The QCD Vacuum, Hadrons and Superdense Matter" takes the reader from the first encounter with the subject to the front line of research, as quickly as possible.