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