The interaction between atoms and electromagnetic fields is an area of central importance to the investigation of fundamental concepts of quantum mechanics. The authors provide an introduction to the theory concerning this interaction by describing the different forms of the interaction and dealing with how these interactions lead to the formation of dressed states, in the presence of vacuum fluctuations as well as in the presence of external fields. They also cover the role of dressed atoms in quantum measurement theory and the physical interpretation of vacuum radiative effects. Treating a key field on the boundary between quantum optics and quantum electrodynamics, the book will be of great use to graduate students, as well as to established experimentalists and theorists, in either of these areas.