This unique book presents a unified, in-depth study of phenomena in photon-matter interactions over a range of many orders of energy. It provides a thorough treatment of relativistic quantum electrodynamics from the quantum field theoretic approach, together with non-relativistic theory in both confined and unconfined geometries. The predictions of QED have been verified to a greater accuracy than any other physical theory. Moreover QED is a paradigm for other gauge theories, and it is presented in such a way that the generalization to other gauge theories is natural. Gauge and Poincare...