This book presents an introduction to quantum mechanics that consistently uses the methods of operator theory, allowing readers to develop a physical understanding of quantum mechanical systems. The methods of operator theory are discussed throughout the book and presented with a mathematically rigorous approach. The author describes in detail how to use the methods of operator theory for analyzing quantum mechanical systems, starting with the definition of the involved physical operators (observables) up to the calculation of their spectra, spectral measures, and functional calculus. In...