This book provides a thorough introduction to the interaction of atoms and atomic ions with optical and magnetic fields. Particular emphasis is placed on the wealth of important multilevel effects, where atomic vapours exhibit anisotropic behaviour. As well as covering the classic two-level atom approach to light-atom interactions, a general multi-level formalism is also described in detail, and used to discuss optical pumping, two-dimensional spectroscopy and nonlinear optical dynamics. The final chapter deals with the mechanical effects of light, including the cooling and trapping of atoms. With full theoretical and experimental coverage, and over 250 illustrations, the book will be of great interest to graduate students of laser spectroscopy, quantum electronics and quantum optics, and to researchers in these fields.