ABSTRACT
Differentiated integration (or differentiation) has been a subject of political and academic debates for a long time, and it ‘has also become an important and – most probably – permanent feature of European integration’ (Holzinger and Schimmelfennig 2012: 293). Recent research goes even further by defining the European Union (EU) as a ‘system of differentiated integration’ constituted by an ‘organizational and member state core but with a level of centralization and territorial extension that vary by function’ (Leuffen et al. 2013: 10). Others have characterized the entire process of European integration as a potential ‘condominio’, ‘based on variation in both territorial and functional constituencies’ (Schmitter 1969: 136) or as an ‘onion’, by visualizing a Europe that is not only segmented by ‘policy areas and levels of government . . . but also by subgroups of European states’ (De Neve 2007: 504). Nonetheless, there is little systematic knowledge about differentiated integration (Holzinger and Schimmelfennig 2012), and yet an ‘excess of terminology’ (Stubb 1996: 283).
