Computer games are now becoming ways to communicate, teach, and influence attitudes and behavior. In this article, we address the role of humor in computer games, especially in support of serious purposes. We begin with a review of the main theories of humor, including superiority, incongruity, and relief. These theories and their interrelationships do well in helping us understand the humor process, but they have been developed in the context of traditional human activity. To explore how they relate to computer games, we present the findings of a qualitative study of player experience of humor and show how it relates to the theoretical perspectives. We then review the main functions of humor, especially its effects on social, emotional, and cognitive behavior. We show how each of these functions can be used in game design to support the specific experiences and outcomes of game-play. Finally, we address the issue of serious games and make suggestions on how humor can inform and support the design of those games. We suggest that humor can support design by smoothing and sustaining the game mechanics. Moreover, games can draw on the functions of humor in the real world for enhancing communication, learning, and social presence. Using humor makes games richer and more powerful, as well as fun. (Contains 1 table.)