Written by a renowned professor of physics, this introductory text is geared toward graduate students taking a year-long course in quantum mechanics in which the third quarter is devoted to relativistic wave equations and field theory. Difficult concepts are introduced gradually, and the theory is applied to physically interesting problems. After an introductory chapter on the formation of quantum mechanics, the treatment advances to examinations of the quantum theory of the free electromagnetic field, the interaction of radiation and matter, second quantization, the interaction of quantized fields, and quantum electrodynamics. Additional topics include the theory of beta decay, particles that interact among themselves, quasi particles in plasmas and metals, and the problem of infinities in quantum electrodynamics. The Appendix contains selected answers to problems that appear throughout the text.