Abstract Within the Better Regulation programme of the EU, co-regulation is promoted as an important strategy to improve the regulatory environment within Europe. It is assumed that co-regulation can enhance the legitimacy of EU governance in the field where this strategy is used. The purpose of this article is to assess the truth of this premise and to analyse whether co-regulation strengthens the legitimacy of EU governance. To this end, the criteria of input and output legitimacy are applied to the European social dialogue as a form of co-regulation in the EU policy area of social law. In this article, a link is made between the tendency to prescribe co-regulation as a specific regulatory strategy in EU legislative policy and the existing knowledge on the purposes and effects of co-regulation and the conditions under which co-regulation can function as a regulation strategy.