Recent empirical evidence suggests that the updated DeLone and McLean's information systems (D&M IS) model can identify the determinants of success of online communities in terms of member loyalty (Lin and Lee 2006). This study is similarly concerned with the challenge of identifying the determinants of success of online communities, but it explores the problem in terms of members' perceived professional development. A qualitative case study was adopted in this study to gather rich and naturalistic data. Online observation and interview data were gathered from three online communities: nurses, web developers and literacy educators. Results reveal seven determinants of success: a willingness to share knowledge, high-quality content, diversity of views, technology, relevant discussions, a respectful environment and rapid response to members' queries. Contributing factors that lead to some of the identified determinants were also found. Implications of the findings and suggestions for future research are provided. (Contains 2 figures and 2 tables.)