Focused on the experts groups of the European Commission, this article aims to understand not only who the European experts are, but also on what grounds. It adopts a sociological perspective, paying attention to the social properties of those actors, in order to better grasp which type of actors can gain access to the European policy-making process by this way, but also how the experts' authority can get the upper hand in the European arena, and under what conditions it may be exerted. (...)