Both the interpretation of atomic spectra and the application of atomic spectroscopy to current problems in astrophysics, laser physics, and thermonuclear plasmas require a thorough knowledge of the Slater—Condon theory of atomic structure and spectra. This book gathers together aspects of the theory that are widely scattered in the literature and augments them to produce a coherent set of closed—form equations suitable both for computer calculations on cases of arbitrary complexity and for hand calculations for very simple cases.