This book presents a collection of papers, written during the last 33 years by Claude Cohen-Tannoudji and his collaborators, on various physical effects which can be observed on atoms interacting with electromagnetic fields. It consists of a personal selection of review papers, lectures given at schools, as well as original experimental and theoretical papers. Emphasis is put on physical mechanisms and on general approaches, such as the dressed atom approach, having a wide range of applications. Various topics are discussed, such as light shifts, level crossing resonances, multiphoton processes, resonance fluorescence in intense laser fields, photon correlations, quantum jumps, radiative corrections, laser cooling and trapping.This volume includes short introductions by the author. Each paper presented in the volume is preceded by a short commentary giving its motivations, explaining how it fits with the general evolution of the research field, and pointing out connections existing between works done at different periods.