Numerous researchers have written about the social dynamics of player communities in multiplayer online games. Following a systematic review of refereed empirical research publications from 2000-2010, this article synthesizes the key methods and concepts researchers have used to study and characterize player communities, as well as the aspects and operationalizations they have concentrated on. The analysis shows that qualitative approaches have been more popular than quantitative. The concepts used to characterize player communities were often not clearly defined or overlapped in meaning. Yet they revealed a prevalence of micro (groups or teams), meso (guilds or organizations) and macro (communities and networks) perspectives. Eighteen different aspects and operationalizations of player communities were identified. Six of these were clearly most popular, i.e. social structuring, rationale, culture & social norms, used ICTs, number of members and time of existence. The article concludes with several perspectives and suggestions for future research.