This monograph presents a complete guide to the theory of modern spectroscopy of atoms. Atomic spectroscopy continues to be one of the most important subjects of contemporary physics. 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 published mainly in Russian and are therefore almost unknown to western scientists. Primarily a reference for researchers and graduate students in atomic physics and physical chemistry, this work will also be of value to physicists and chemists in other areas who use spectroscopy in their work.