Differentiated integration in the EU – what do the member states ‘think’ about it?

A growing literature is studying the phenomenon of differentiated integration (DI) in the European Union (EU). Empirical studies have focused on charting the degree of existing differentiation, often understood as exemptions from common EU rules. The present report seeks to complement this literature in two ways: first, the report develops a holistic conceptualization of DI by distinguishing between polity and policy differentiation. Similarly, we distinguish two mechanisms through which differentiation can be realized, one satisfying demand for the status quo (‘opt-outs’) and the other satisfying demand for more integration (‘enhanced cooperation’). Second, the existing literature has paid relatively little attention to what the EU member states actually ‘think’ about DI. We contend that member states’ preferences about DI cannot be read off of differentiated EU rules, given that institutional rules and international bargaining processes intervene. Therefore, the report poses two empirical questions: What positions do EU member states take on DI? And why? To answer these questions, the report uses new data from 27 member states on expressed governmental preferences about differentiated integration between 2008-2020. With regard to the first question (WHAT), our findings are threefold: First, polity differentiation is seen slightly negatively on average by the member states. Second, there is significant cross-country variation in member state preferences toward polity differentiation. Third, the mechanism of ‘enhanced cooperation’ is viewed much more favourably than the ‘opt-out’ mechanism. With regard to the second question (WHY), our findings are twofold: First, member states’ positions are not only or predominantly determined by their structural characteristics (e.g. size, wealth, identity), but rather by the expected impact of DI on polity legitimacy and effectiveness. The second key finding is rooted in the inductive identification of factors that have not yet been prominently discussed in the literature. We find that ‘integration experience’, different ‘visions of the EU’, and the ‘shadow of polity DI’ play a role in how EU member states assess differentiated integration. Overall, these factors point to the conclusion that the formation of member state preferences does not happen in a vacuum but is strongly influenced by existing or expected European interdependences.