Drawing on evolutionary theory, the author questions which cognitive processes underlie the capacities to play and to pretend play and the degree to which they are present in both humans and nonhuman animals. Considering cognitive capacities not all-or-nothing phenomena, she argues they are present in varying degrees in a wide range of species. Recognizing the risks involved in comparative studies, she identifies the unique features of cognition underlying pretend play while describing the broader phylogenetic sources from which they come. In the end, she finds, although play based on particular degrees of memory, perception, and consciousness can be found in many species, pretend play depends on distinctive degrees of memory, imagination, and metacognition--a cognitive process she calls "reflective imagination"--and appears characteristically human.