Rough-and-tumble play, or play fighting, is common in the young of many mammals. Research on play fighting among rats shows that there are many levels of neural control over this behavior: subcortical mechanisms mediate the motivation and behavior of such play, and the cortex provides mechanisms by which the play changes with age and context. The cortical mechanisms help to explain the advantages playing offers the brain. The cortically induced modulations of the content of play with age ensure that exposure to particular kinds of experiences are enhanced during the critical juvenile period. These experiences, in turn, modify the development of other areas of the cortex. Such cortical changes appear to mediate the effects of play on the refinement of social skills. As a result, rats that play as juveniles are more socially competent as adults. This work was supported by the Natural Sciences and Engineering Research Council of Canada and the Alberta Heritage Foundation for Medical Research.