"The term 'play' has long been a linguistic waste-paper basket for behavior which looks voluntary but seems to have no biological or social use. What counts as 'play'? What explanations have been given for it, and how far are they adequate? Why do children and the young of many animal species play? To answer such questions Susanna Millar here discusses psychological theories about play and reviews observational and experimental studies of the play of animals of different evolutionary development, of children at different ages, in different cultures, and in therapy. She relates different forms of play to a number of underlying behavioral mechanisms which modern methods of experimental psychology are beginning to uncover. Susanna Millar argues that play has a variety of biological functions related to childhood development and other specific conditions."-Publisher.