Commercial enterprises are increasingly using online communities to allow customers to interact with each other before and after a purchase, and television shows are using them to get a closer grip on the audience. Although they have been around since the foundation of the Internet, little research has been done to understand the communicative interactions that arise within such online communities. In this paper, we use the notion of genres to study the communicative practices of three emergent online Internet communities at a university in the United States. Genres are organizing structures shaped by the communicative actions of individuals, and they provide an analytical lens to investigate those actions (Orlikowski and Yates 1994a, 1994b). We find that a parsimonious set of only six genres is needed to adequately classify almost 1,250 communications between the members of our three communities. Evidence also suggests that three of these genres are essential foundation blocks for communication in online communities. We also witness unmediated, explicit structuring of a genre, and the increase in participation this generates, which provides insight for those building and managing online communities. This study shows that genre analysis is a powerful tool to assist in understanding emergent online communities and we provide insight into how its use may facilitate growth and participation in the community.