The paper reports a field study of knowledge sharing in a large and complex organization. The objective of the study was to gain an in-depth understanding of the implementation and use of a web-based knowledge sharing system designed to facilitate the circulation of best practices among middle managers. We followed the system from its introduction in early 1997 until it was abandoned in the beginning of 2000. We focused on the way the system was introduced in the organization, how it changed, and how the intended group of users received (and eventually rejected) the system. Based on our interviews and observations we identify five reasons for the systems failure. We close the paper by some reflections on the use of the concept of “shared practice” in the development of IT-supported knowledge sharing systems.