PLAY! is a reflection on the culture of playground design. Urban playgrounds form a vast, intricate spatial and social network. Increasingly designed from standards and regulations, and under pressure in the limited urban space, they tend to disappear into the background. Yet, they are also spaces where material innovation happens, that become a stage of new professional collaborations, and that carry so much hidden social, spatial, climate mitigation, and nature positive design potential. With a photo documentation of over 200 playgrounds across Rotterdam, PLAY! records and reflects on the accumulated urban environment of play, an amalgamation of ideas, dreams, and attempts, annotated with insights from interviews with playground makers, designers, and urban thinkers. Through local stories, the book draws attention to emerging progressive practices, concepts, and ideas, as the beginning of a conversation about possible futures of urban play landscapes.