The emergence of online communities has brought a profound impact on human interaction and methods of information exchange in society. More than one-third of all U.S. Internet users have turned to mass, large-scale communication systems such as e-mail, mailing lists, instant messaging, chat rooms, Web stores, customer service sites, and threaded discussion systems such as USENET (Preece, 2002). Reflecting this prominent phenomenon, there have been a considerable number of studies focused on online communities and communications. This article focuses on the factors and dynamics of the knowledge creation process in online communities, relying on Nonaka’s Socialization-Externalization-Combination-Internalization (SECI) Model (1994). Based on that framework, this article discusses the factors that affect knowledge creation and sharing in online communities. The rest of this article is organized as follows. The characteristics of online communities are discussed in the “Background” section. The section titled “Dynamics of Knowledge Creation and Sharing in Online Communities” reviews the existing concepts and the SECI model of knowledge creation, and extends that model to include the online community context. We further discuss the effects of important factors on knowledge creation and sharing in online communities. The section “Future Trends” suggests further research opportunities in the area. The final section summarizes and concludes the article.