The legitimacy of the European Commission expert groups is given for the expert groups generally - the European Commission points to improving the knowledge base for better policies as the main motive for involving its expert groups in policy making. However, as there is large variation between the groups in terms of objectives, group composition, policy area, etc., one would also expect variation in terms of how the groups work and which outcomes result from their meetings. Arguably, some groups can more easily be legitimized as knowledge providers than others. In this paper, the differences between a selection of the expert groups of the European Commission is analysed by looking at meeting minutes. By linking the variance found to differences in policy area, group composition, and objectives, the paper discusses both the legitimacy of these groups as knowledge providers as well as what "expertise" can mean in different settings.