Publications devoted to the polarization of the quantum states of ensembles of atomic particles in ionized gases and plasmas are reviewed. A theoretical description of the phenomenon is given and its relationship to anisotropic properties of plasmas is established. Methods of determining the polarization of the states of atomic ensembles from the polarization of the line spectrum of excited particles are described. Experimental studies of gas discharges, beam-plasma systems, and astrophysical objects are summarized. It is shown that the polarization of the quantum states of atoms can be observed over a wide range of plasma conditions.