Play has long been considered an enigmatic behavior that is hard to define, but having many putative functions difficult to confirm. This situation is changing quite rapidly in recent years. This introduction to a special issue on play provides some general background, historical and contemporary, on the recognition and phylogenetic aspects of play, along with a discussion on the adaptive functions of play and some recent research findings that might facilitate or extend future research.
In this short introduction I have tried to present a few selective comments on the fascinating phenomena of play. It is clear that play in a wide variety of species is being increasingly studied in detail by many laboratories. Although disparate phenomena at one level, I think it important that those working on social play keep up with the literature on other types of play and vice versa. Similarly, those working on play in children should know what is being done in primate play and those working with nonhuman primates should keep up with those working on carnivores, rodents, birds, and nontraditional species. Again, such interests need to be reciprocated. Play research, as an interdisciplinary field, benefits greatly from findings in many other fields and researchers need to keep abreast of these trends and accommodate new theoretical and methodological approaches that have, and will continue to, enrich our understanding.