This monograph presents a comprehensive description of the theoretical foundations and experimental applications of spectroscopic methods in plasma physics research. The first three chapters introduce the classical and quantum theory of radiation, with detailed descriptions of line strengths and high density effects. The next chapter describes theoretical and experimental aspects of spectral line broadening. The following five chapters are concerned with continuous spectra, level kinetics and cross sections, thermodynamic equilibrium relations, radiative energy transfer, and radiative energy...