In June of 2016, the Chicago Zoological Society–Brookfield Zoo hosted the Psychonomic Society Leading Edge Workshop on The Evolutionary and Psychological Significance of Play. In a partnership between the Chicago Zoological Society, American Museum of Natural History in New York, and the University of Southern Mississippi, we brought together sixteen of the leading experts from a diversity of fields that study play. The goal of the workshop was to examine the evolutionary and psychological significance of play while increasing interest in cross-disciplinary research. The following special issue highlights many of the discussion points throughout the workshop, starting with an exploration of common terminology and definitional criteria.

Behavioral observations and experiments are guided by increasingly theoretical questions to test ideas about what, how, and, ultimately, why play occurs. Certain types of play are understood well enough to theorize convincingly that there is a particular psychological or evolutionary significance. For example, children’s imaginary play research is grounded in a long tradition of developmental psychology and ideas about its psychological significance. But, in contrast, adult game play is studied in cognitive psychology with increasing evidence that its significance is minimal in terms of cognitive transfer, while its social significance does not seem generalizable across cultural groups.

This splitting of fields might appear to create an unwanted contradiction, but rather it is a useful outcome of bringing scholars together. It allows for a better understanding of specific behaviors, reveals the limitations of current research, and highlights possibilities for future investigation.

The crossing of the divides, often one of the noble goals for multidisciplinary meetings, is visible in other ways. Research on imaginary companions that suggests play to be useful for later adaptive social functioning strikes a chord with research on mammalian social play. The paucity of research on crocodilian play, because of its rare occurrence, is mirrored in limited descriptive research on board games, as they have often been overlooked by anthropologists. The different disciplines share theoretical questions, descriptive limitations, as well as the same diversity of play that make generalizations so problematic.

As confirmed by several authors in this volume, there is a wide assortment or diversity of play. This includes everything from play in cetaceans, rats, and dogs to board games and imaginary play in humans. Given the diversity of topics and frequency of research, the importance of play behavior remains elusive. There is growing consensus among scholars of play that the phenomenon may be too diverse and complex to capture in one all-encompassing theory. Considering the different species, types of play, and contexts, there is little reason to assume that all play shares the same universal significance. This notion is highlighted among the contributions of this special issue.