The debate on the European Union’s legitimacy crisis led to the discovery of civil society in EU governance. With the waning of the permissive consensus, politicians, bureaucrats, and academics shifted their attention towards the input-oriented dimension of democratic legitimacy which results from authentic participation and governance ‘by the people’. Participatory democracy via civil society involvement came to be considered as a promising supplement to representative democracy and entered EU documents such as the White Paper on European Governance and the draft Constitutional Treaty around the turn of the millennium. However, the origins of the current debate on civil society in EU governance can also be traced back to interest group research which has flourished since the early 1980s and the debate on ‘participatory governance’ that unfolded in the 1990s. These approaches are more concerned with effective political problem-solving and the output-dimension of democratic legitimacy which can, from this point of view, be improved by stakeholder participation and civil society engagement. In fact, two scholars who refer to ‘civil society’ do not necessarily mean the same thing and this is even less obvious if journalists, politicians or public officials allude to civil society. In order to enhance the basis of the discussion, we should seek to identify the conceptions they rely on. This will help us to understand where different arguments come from. Hence, this essay seeks to identify the different layers of the current debate on civil society participation in EU governance by unfolding the traditions of thought academic and political advocates of civil society in EU affairs currently draw on. This essay will basically distinguish between output-oriented approaches which explore the contribution of civil society groups to effective governance and problem-solving on the one hand and research that is interested in input-oriented legitimacy and participatory democracy on the other.