Providing an accessible textbook, this volume illustrates the intimate connection between quantum mechanics and QED in two steps: first the quantization of free fields and then their interactions. The text contains solved problems to facilitate the application of the theory presented, as well as a useful appendix on the theory of distributions. The description of the quantization of various fields, and the clear presentation of theory and the most important interaction processes in QED make this textbook a useful guide for those studying physics at both the graduate and undergraduate level.