Designed for advanced undergraduate or beginning graduate students and requiring no prior knowledge of the subject, this book introduces quantum field theory, exploring topics that include the quantization of fields, S-matrix theory, Feynman diagrams, calculation of decay rates and cross sections, renormalization, symmetries, and symmetry breaking. The authors include some background material, particularly on classical field theory and group theory needed for the exposition. They also provide detailed calculations of weak and electromagnetic processes and many exercise problems. This edition revises some of the notation, clarifies some explanations, and incorporates answers to selected problems.