The popular book Theoretical Physics is now being offered for the first time in corrected and expanded form in individual volumes. This allows students to easily carry and use the handy volumes for studying, solving problems, and quick reference. At the same time, the entire theoretical physics curriculum of the bachelor's program (and beyond) is presented in a coordinated manner across the four volumes. This book is the third part of the four-volume series and comprehensively covers the curriculum of the bachelor's lecture on quantum mechanics at major universities in Germany, Austria, and Switzerland. The particular strength of this series lies in its support for the reader through a variety of didactic elements: Each chapter begins with fundamental questions, and important statements, formulas, and definitions are clearly highlighted.