We probably all have a pretty good intuitive notion of what a game is. The general term "game" encompasses board games like chess and Monopoly, card games like poker and blackjack, casino games like roulette and slot machines, military war games, computer games, various kinds of play among children, and the list goes on. In academia we sometimes speak of game theory, in which multiple agents select strategies and tactics in order to maximize their gains within the framework of a well-defined set of game rules. When used in the context of console or computer-based entertainment, the word "game" usually conjures images of a three-dimensional virtual world featuring a humanoid, animal or vehicle as the main character under player control. (Or for the old geezers among us, perhaps it brings to mind images of two-dimensional classics like Pong, Pac-Man, or Donkey Kong.) In his excellent book, A Theory of Fun for Game Design, Raph Koster defines a game to be an interactive experience that provides the player with an increasingly challenging sequence of patterns which he or she learns and eventually masters. Koster's asser-tion is that the activities of learning and mastering are at the heart of what we call "fun," just as a joke becomes funny at the moment we "get it" by recognizing the pattern.