Computer-based games have become an important social phenomenon of modern society. Fast-growing online games are becoming the dominant sector in computer-based games. The development of online games involves many disparate disciplines from the technology, entertainment, and behavior sciences. Attracted by the potential impact of this rapidly growing segment, there is a growing literature addressing this fascinating topic. However, the scope, perspective, and main research themes of online games study are still unclear to date. Therefore, we utilized the intellectual structure technique developed by the information scientist to help clarify the scope and themes of this research domain. We analyzed thousands of relevant literature and tentatively identified 25 main research themes to facilitate the comprehension and study of online games. A research framework is developed by synthesizing the research themes and references. The framework encompasses research areas in network infrastructure, game platform architecture, game applications, player study, ICT mediated social activities, social capital, and game business models.