The 60th Anniversary of the EU was marked by the declaration that the future of the Union might lie in more differentiated integration (DI). Likewise, the European Commission’s White Paper on the future of Europe favoured greater DI. The appeal of DI lies in its allowing some member states (MS) to integrate further, while others can temporarily or permanently opt out of specific policies that may be difficult for them to implement. As a result MS have different rights and obligations in regard to specific EU policies. Whilst there now is abundant conceptual work on DI as well as a few empirical studies, DI to date has not been sufficiently theorised using existing theories of European integration, thereby remaining somewhat disconnected from integration theory. This paper engages with this gap by exploring how three established theories of European integration (would) address the question of fairness in institutional design as regards DI: liberal intergovernmentalism, neo-functionalism and demoicracy. After sketching the debate about more DI, we will first discuss which understandings of fairness in international cooperation these approaches entail. In short, liberal intergovenmentalists prioritise interests of states, neo-functionalists interests of citizens, and demoicrats try to balance fair treatment of the two. In a second step, we will apply the three approaches to concrete questions of procedural and substantial fairness in institutional design as regards DI, thereby sketching the political options that can be derived from the three approaches.
