The socializing functions of nonhuman primate play behavior are discussed. An evolutionary perspective of play behavior is presented to provide a concise view of its importance in primate phylogeny. Some of the major variables influencing play behavior's socializing functions, i.e., gender, age, group structure and population dynamics, and the econiche, are reviewed. It is concluded that the major socializing functions of play behavior include proper social development, setting the basis for the adult dominance hierarchy, social integration of individuals into the group structure, and learning the social communicatory matrix.