This paper proposes a context-based approach of social networks and virtual communities in the enterprise area. We point out that making context explicit it is possible to provide a global picture of the main aspects of social networks. A first result of this study is that the explicit consideration of contexts--especially shared contexts--could improve notably the collaborative-work processes in an enterprise. A second result shows the interest of considering simultaneously the paradigms of context and social network when IT is at the core of the enterprise. A third result is to point out that different types of context account for the flux of information between groups as well as inside each group. Finally, we point out that it is preferable to speak of contextualizations of a social network rather than virtual communities.