After an introduction to relativistic quantum mechanics, which lays the foundation for the rest of the text, the author moves on to the phenomenology and physics of fundamental interactions via a detailed discussion of the empirical principles of unified theories of strong, electromagnetic, and weak interactions. There then follows a development of local gauge theories and the minimal standard model of the fundamental interactions together with their characteristic applications. The book concludes with further possibilities and the theory of interactions for elementary particles probing complex nuclei. Numerous exercises with solutions make this an ideal text for graduate courses on quantum mechanics and elementary particle physics.