How have the ways we imagine and understand games changed since World War II? Play and games, although inextricably connected, have come to mean quite different things in the early twenty-first century popular culture, and I argue that this change is a cultural product of The Cold War. Today, games are described as products, systems, and even rituals. It is assumed that all games have rules, and these rules are shared through code, manuals, and sometimes oral tradition. Whereas games are systems, play is the embodied phenomenon associated with navigating such systems. Play relates specifically to bodies, and is often—though not necessarily always—connected to games. The nature of games and play is generally agreed upon in both popular discourse and by game studies scholarship. People play games, people play with each other, and the essence of play cannot be reduced to any one product, container, system of rules, or even social ritual. Rules may contort the dynamics of play, but they cannot define the essence of the phenomenon. Building on these distinctions, this dissertation claims, first, that our definitions of games and play are discursively contingent. Second, it develops this point by showing how in the latter half of the twentieth century, games began to be explicitly valorized over play. Games are typically seen as valuable, productive, and potentially transformative, while play is normally associated with leisurely, childish, and chaotic behavior. Third, alongside the valorization of games over play there has emerged a discourse that this dissertation terms the ludic imagination in which “truth” is conflated with quantitative and competitive logics. The ludic imagination contributes to other studies of the Cold War by focusing on the value placed on rationality as well as the affects of isolation and fear that characterize the era’s popular culture and military policy. I use correspondence, internal reports and memos from the RAND Corporation Archive and The MIT Center for International Studies, as well as hobby publications and trade publications from The Ray Browne Popular Culture Archive and the Dragon Magazine CD-ROM Archive in order to reveal a historical arc that connects military ideology around games and play to popular culture. This arc includes documentation from the RAND Corporation, correspondence within a grassroots network of gamers that included play-by-mail Diplomacy hobbyists, and the design notes of Dungeons & Dragons players. Through these primary sources, I show how networks of military elites at the RAND Corporation overlapped with networks of grassroots hobbyists and together imagined the intersection of games and play. This reading evaluates the limits of these terms by considering how racism, sexism, and homophobia collude with the quantitative and essentialist worldview of military logistics. Here I evaluate the indebtedness of the ludic imagination to a reductionist and pragmatist military ideology and consider what potentials exist to play with its future definition.