Online Communities have been researched for a long time from social, informational as well as economic perspectives. Most approaches up-to-now focussed on the interaction of a number of users with specific communities, are studies about the characteristics of communities in different domains or are general guidelines for the development of these communities. These approaches, however, neglect the aspect that one entire online community is embedded in a landscape of other communities and interrelates with them. In this article we describe this landscape as a market in which a community competes with other communities for online members. We discuss characteristics and forces of this market and present results from a study that monitored 36 online travel communities over a period of several months. Our data indicate that with regards to registered members, there are few very large communities, in contrast to a large number of very small communities. An analysis of the average number of members that are actually online, however, shows that smaller communities (e.g., with a regional scope) are, in principle, able to mobilize a higher degree of their members. We conclude that niche strategies can be successful in this market, and discuss implications for this community landscape.