Spectra are fundamental characteristics of atoms and ions, and are the main source of information on their structure and properties. This monograph presents a complete guide to the theory of modern spectroscopy of atoms. The book describes the contemporary state of the theory of many-electron atoms and ions, the peculiarities of their structure and spectra, the processes of their interaction with radiation, and some of the applications of atomic spectroscopy. It contains a large number of new results, which have been mainly published in Russian and are therefore almost unknown to Western scientists. A graduate level text and research reference, this book is aimed primarily at atomic physicists and physical chemists, but will also be of value to physicists and chemists in other areas who use spectroscopy in their work.