This study focuses on knowledge sharing in large, complex organizations. The study examines the introduction and use of a Web-based system designed to facilitate the circulating of best practices among middle managers in a multi-national pharmaceutical company. Despite strong commitment from senior management and several attempts to redesign and reinvent the system over a three-year period, implementation of the system eventually failed. We found that managers generally gave four reasons for not using the system: (1) time pressure; (2) lack of incentives; (3) the problem of “bragging”; and (4) the importance of personal networks. A more important finding is that the group of managers in this company did not constitute a single, uniform entity, a coherent “community of practice”, and that the divisions within the group hampered meaningful communication and knowledge sharing. We suggest that these difficulties reflect the more general problem of communicating across the boundaries of different practices and communities of knowing.