As in any social organization, people need to invest effort in the health of their online groups. Electronic mailing list servers, such as LISTSERV and Majordomo, and other such groups need people to maintain the technology infrastructure, carry out social management tasks, and recruit new members. Members must read and contribute to discussion. Here, we ask why people do this. In many online groups, preexisting social ties and material benefits for contributions are weak or nonexistent. In this chapter, we consider how the formal leadership role, personal and community benefits, and community characteristics influence the effort members put into helping their online groups. Results from a survey of Internet mailing list owners and other members suggest that although owners, who have a formal leadership role, do more of the effortful community building work than do regular members, other members also take on some of the work. Moreover, members who value different benefits are likely to contribute to the development of an online community in different ways.