The impulse toward play is very ancient, not only pre-cultural but pre-human; zoologists have identified play behaviors in turtles and in chimpanzees. Games have existed since antiquity; 5,000-year-old board games have been recovered from Egyptian tombs. And yet we still lack a critical language for thinking about play. Game designers are better at answering small questions ("Why is this battle boring?") than big ones ("What does this game mean?"). In this book, the game designer Brian Upton analyzes the experience of play--how playful activities unfold from moment to moment and how the rules we adopt constrain that unfolding. Drawing on games that range from Monopoly to Dungeons & Dragons to Guitar Hero, Upton develops a framework for understanding play, introducing a set of critical tools that can help us analyze games and game designs and identify ways in which they succeed or fail.