Interactive immersive entertainment, or videogame playing, has emerged as a major entertainment and educational medium. As research and development initiatives proliferate, educational researchers might benefit by developing more grounded theories about them. This article argues for framing game play as a "designed experience." Players' understandings are developed through cycles of performance within the gameworlds, which instantiate particular theories of the world (ideological worlds). Players develop new identities both through game play and through the gaming communities in which these identities are enacted. Thus research that examines game-based learning needs to account for both kinds of interactions within the gameworld and in broader social contexts. Examples from curriculum developed for "Civilization III" and "Supercharged!" show how games can communicate powerful ideas and open new identity trajectories for learners. (Contains 2 figures and 1 table.)