Educational games and simulations can engage students in higher-level cognitive thinking, such as interpreting, analyzing, discovering, evaluating, acting, and problem solving. Recent technical advances in multiplayer, user-created virtual worlds have significantly expanded the capabilities of user interaction and development within these simulated worlds. This ability to develop and interact with your own simulated world offers many new and exciting educational possibilities. This article explores the technical capabilities and educational potential of these new worlds. Additionally, it presents and illustrates a model, which uses interaction combinations, to identify course content and topics having educational applications in virtual worlds. The EDUCAUSE National Learning Infrastructure Initiative (NLII) has identified games and simulations as an emerging key theme affecting teaching and learning. Virtually all college students have had experience with games. Games represent active, immersive learning environments where users integrate information to solve a problem. Learning in this manner incorporates discovery, analysis, interpretation, and performance as well as physical and mental activity. An increasing number of 116 Association for the Advancement of Computing In Education Journal, 16(2) colleges and universities are exploring the use of games to enhance learning. (EDUCAUSE-NLII, 2004, p. 28) Recent technical advances in massively-multiplayer, user-created virtual worlds, such as Second Life, Active Worlds, and There, have made this technology both affordable and accessible. Additionally, these advances have expanded the capabilities of user interaction and development within these simulated worlds. Unlike most computer games, even multiplayer games, these virtual worlds allows the users to create their own world and interact with it and with other users in it, rather than simply interacting with an existing, preprogrammed world. This ability to develop and interact with your own simulated world offers many new and exciting educational possibilities. With user-created virtual worlds, educators can create their own simulated worlds and have their students learn by exploring, interacting, and reflecting on their experiences in this world. Alternatively, students can actively apply course content and problem solve as they create and interact with their own worlds.