Play behavior and playfulness may be major factors in behavioral and cultural evolution in animals, and especially people. Although play is largely ignored by scholars and scientists dealing with human cultural evolution, this chapter argues that it is an ancient and deep phenomenon that has appeared repeatedly throughout evolution, is at the root of many behavioral and social phenomena, and ignoring it fosters a myriad of often incompatible scenarios. For example, play and ritual seem to be disparate phenomena, one focused on freedom and variety, the other on formality and rigidity. In reality, they have many common elements, and play may be a source for not only rituals in animals, but also cultural attainments in humans including language, tools and other innovations, morality, religion, science, as well as other aspects of our lives typically viewed through an anthropocentric lens. Surplus Resource Theory helps explain the organismal and setting conditions for play behavior in many species and the cultural attainments of humans and thus aids integration across academic fields. The playful origin of religion, as posited by Robert Bellah in his treatise Religion in Human Evolution, is highlighted.