A Community of Practice (CoP) is an organizational form receiving increasing attention as a structure for sense making, knowledge management and learning. The central question addressed in this article is how and why these communities form and grow over time. These questions are explored through a qualitative analysis of a CoP formed to help knowledge management practitioners. In this case study, a description of how the organization formed, survived, grew and matured over a five-year period (1999-2004) is given. Several practices and structures related to CoP development are identified; for example, operations, roles and responsibilities, communications, sub-group structures, use of information technologies and other aspects of organizing. Using data from several sources (e.g., membership surveys, interviews with key informants, document analysis), four sets of factors that have helped this organization succeed are identified: Individual, Content, Meeting and Organizational. These factors are arranged into a preliminary descriptive model of the function and structure of CoPs over the life cycle. To practitioners, the work sheds light on how to set up and successfully grow a community of practice.