Welcome to the American Journal of Play special issue on free play, another in our series of theme issues that appear from time to time. Each focuses on an important topic in the fast-developing study of play. Each is guest edited by a distinguished expert on the topic. And each includes work by the leading researchers and thinkers on the topic. Guest-editor Peter Gray, author of the popular textbook Psychology and the widely read Psychology Today blog “Freedom to Learn,” assembled this issue with participants of “Empowering Neighborhoods and Restoring Play,” a symposium held in 2010 in Binghamton, New York, using work from them inspired by that conference. This special issue begins, then, with an interview of journalists Hara Estroff Marano and Lenore Skenazy, who diagnose the current fearful climate that deprives children of the mental, physical, and social benefits of playing. In the first of two articles, Gray follows the correlation between the sharp decline of free play and the steep rise in psychopathology in children and adolescents. In a second contribution, he describes the virtues of “age-mixed” play that, until very recently, characterized the free time of children. Evolutionary psychologist Peter La Freniere explores the heritage of play among mammals, noting how humans, especially boys, learn to regulate emotion through rough-and-tumble play. Anthropologist David F. Lancy examines rule making and rule breaking in the game of marbles to discover the roots of a crafty human intelligence and the dividends of playing outside the reach of interfering parents. Evolutionary biologist David Sloan Wilson, along with Danielle Marshall of the community playground-building group KaBOOM! and Hindi Isherhoff of Portland’s innovative City Repair initiative examine the organizational dynamics of creating successful play spaces. Wilson also provides an overview of the inventive Design Your Own Park Competition through which scholars, city planners, and funders enable neighborhoods to turn vacant urban spaces into parks and playgrounds. Taken together, these articles argue fervently for the value of free play and the urgency of restoring it.