The Internet now hosts an ever-increasing collection of tools (e.g., list-servers, discussion groups, chat rooms, bulletin boards, social networking sites, and wikis) that help people connect, communicate, and collaborate. The development of these technological tools, together with the desire to capitalize on the collective efforts of like-minded individuals has led to the formation of a wide variety of online communities. While some community oriented ventures have been extremely successful (e.g., MySpace and Wikipedia), this is not the norm. Online communities are faced with significant challenges associated with attracting and maintaining a voluntary membership base---and many fail to do so. The success and failure of these communities lies in their ability to attract and maintain a membership base of users that are willing to participate. A key to attracting and retaining members is to better understand how members join, and how their relationship with the community, impact their behavior in the community. The primary purpose of this dissertation research is to propose and test different aspects of community life that links how people join the community, and the bonds they form with the community, influence their participation in the community. A secondary objective is to expand the conceptualization of participation beyond traditional "frequency of contribution" constructs, to one that incorporates a wider range of community behaviors that need to be performed by a community's members. Towards these objectives, this work examines how two different aspects of community life, joining and commitment, affect different aspects of participation, including content provision, content seeking, and informal moderation. The first study draws on literature of word-of-mouth from marketing and organizational recruiting to explain how community joining processes, specifically member referrals, can shape member participation behaviors. The second study, draws on the organizational commitment literature, to theorize how the member-community relationship impacts member participation. Data to test these models proposed in each study was collected from a large community. The community promotes itself as a "general discussion" community, with the goal of supporting social conversation amongst its members. This dissertation finds that member referrals and community commitment play an important role in members' participation within online communities. These factors exert their influences at different stages of a member's association with a community. Referrals appear to be most influential at the earliest stages of community life, facilitating the return of members after they join and the level of their participation in the short term. This may be useful in helping communities overcome initial judgments of members with respect to the potential value of the community, giving the community a chance. However, communities must also be able to develop committed members to sustain participation in the long term. The commitment that develops between a member and the community influences member's participation, with the various types of commitment (continuance, affective, normative) leading members to participate in different ways. This may be useful in helping community administrators, who face the challenge of achieving an appropriate mix of participation to maintain the quality of the member-generated content pool over time. Taken together the results of the studies presented provide a theoretical foundation for linking relational models of community engagement and content contribution models. In doing so, expands the range of behaviors that should be...