ABSTRACT
This chapter begins by providing a critical review of the 5-criteria definition of play. Although the definition has undoubted advantages, such as discriminating play from other similar behaviors and providing a theoretical scaffold useful to compare play-like behavior across different phylogenetic taxa, some of the criteria are often difficult to apply. Some modifications to those criteria are considered. The second part of the chapter is dedicated to play fighting, the most frequently studied and the most cognitively demanding form of play. The important role of play fighting on the development of the social brain and the involvement of sophisticated forms of communication are discussed in the light of recent empirical findings.
