This article analyses how the concept of representativeness/representativity has been used by the EU Institutions to structure interest intermediation. It examines how the concept has emerged, been defined, and applied. Representativeness is mostly used to refer to organisational features of the interest groups (organisational representativeness), but is occasionally used in relation to representative aspects of the overall system of interest representation (system representativeness). The focus is primarily on aspects of ‘descriptive representativeness’, in particular territorial and thematic representativeness, rather than on ‘procedural representativeness’ that guarantees authorization and accountability. Originally applied to the social partners only, the White Paper on European Governance proposed to extend the use of representativeness to the wider category of civil society organisations. We argue that the application of the concept to civil society organisations proves more problematic than to the social partners. The European Transparency Initiative subsequently abandons representativeness, but contains the seeds for its re-emergence.