This paper outlines a typology for online communities of practice. The typology is based on findings from observations of three online communities of practice, a content analysis of messages, and a review of the existing literature. The three examples of communities of practice are of electronic discussion lists that cover topics of interest to university webmasters, librarians, and educators. This work expands on a typology that consolidated prior research and focused on online communities of practice within organizational settings (Dubé, Bourhis, and Jacob, 2006) by extending it to be inclusive of open online communities of practice that are not constrained by any organizational context. Characterizing communities of practice in this manner enables various aspects of them to be analyzed, which can illuminate ways to support the implementation of effective online communities of practice for specific purposes.