The research on optical phenomena connected with interference of nondegenerate atomic states is reviewed. The main types of phenomena are subdivided into four groups, called pulsed beats, beat resonance, parametric resonance, and phase resonance. Common to all these phenomena is the appearance of modulations in the spontaneous emission of the atoms or in the absorption coefficient of the atomic system. Certain nonlinear manifestations of interference of states are also considered. The possibility of using interference phenomena as methods for the investigation of subtle details of the energy structures of atoms and molecules is considered.