There is interest in various forms of knowledge management, including communities of practice. However, there are no confirmed results on the conditions for success, while organizations expect substantial gains from knowledge development. Communities of practice are seen as a source of knowledge management, and in the end of competitiveness and innovation. The interest arises from this objective of knowledge management and innovation, but it is a specific form of knowledge management, in principle more centred on the individuals and their exchanges than on "management" by the firm, although the firm has a role to play in fostering such initiatives. Thus, the use of communities of practice has emerged as a way to develop collective skills and organizational knowledge, in order to foster innovation and success for organizations. The main contribution of this paper is that it identifies the conditions for success of communities of practice as a mode of knowledge management and knowledge sharing, as these conditions have not been confirmed in previous work. The paper first defines this form of knowledge sharing through communities of practice. It then presents some of the results concerning success, specifically satisfaction and attainment of objectives, as success is defined in this way. This is done on the basis of various case studies of communities of practice which were studied over a period of one year. The empirical results are based on a questionnaire survey administered to the participants of these communities of practice, but also on qualitative interviews and regular work and exchanges with some of the animators/managers and participants in these communities of practice. Some interesting differences are observed according to age and gender, as well as some challenges that were observed in the knowledge-sharing process, and which are often underestimated. The paper identifies some conditions which explain success, defined as attainment of objectives, and these are: commitment and motivation of participants for the attainment of objectives, as well as the presence of a leader, animator or steward. These preconditions for success confirm and extend what is documented in the literature, especially in the seminal work of Wenger and Lave (1991).