An Introduction to Quantum Field Theory is a textbook intended for the graduate physics course covering relativistic quantum mechanics quantum electrodynamics & Feynman diagrams The authors make these subjects accessible through carefully worked examples illustrating the technical aspects of the subject & intuitive explanations of what is going on behind the mathematics After presenting the basics of quantum electrodynamics the authors discuss the theory of renormalization & its relation to statistical mechanics & introduce the renormalization group This discussion sets the stage for a discussion of the physical principles that underlie the fundamental interactions of elementary particle physics & their description by gauge field theories