MUDs (Multi user dungeons / domains) are a type of role-playing adventure game on the Internet. In comparison to the World Wide Web, Newsgroups, or IRC, they are a less well-known type of computer-mediated communication, and the inhabitants of these virtual worlds form a specific subculture in the Internet. Nevertheless, a whole set of sociological and psychological questions can be researched here. In the following contribution, the empirical methods at the researcher’s disposal will be presented. Prior to that, however, the author will clarify what MUDs are and how they differentiate themselves from other forms of CMC (computer mediated communication). Next, the possibilities and limits of MUD research and the various research levels will be discussed. Besides basic problems in defining samples, the pros and cons of the most common and, in this context, frequently used methods of qualitative and quantitative social research will be presented: (participatory) observation, interview and questionnaire based surveys.