This second volume on quantum mechanics by Franz Schwabl discusses nonrelativistic multi-particle systems, relativistic wave equations and relativistic fields. As usual the text follows a compelling mathematical presentation where all intermediate steps are given and where numerous examples for application and exercises help the student to gain thorough knowledge of the subject. The presentation of relativistic wave equations and their symmetries and the fundamentals of quantum field theory lay the foundations for advanced studies in solid-state physics, nuclear and elementary particle physics. The new edition is carefully revised and the special focus on step by step approach is buttressed even more.