Quantum field theory is the basic theory of elementary particle physics. In recent years, many techniques have been developed that extend and clarify this theory. This book develops quantum field theory starting from its foundation in quantum mechanics and incorporates the most modern methods, giving a thoroughly modern pedagogic account that starts from first principles. The path integral formulation is introduced right at the beginning. The method of dimensional continuation is employed to regulate and renormalize the theory. This facilitates the introduction of the concepts of the...