Models of differentiated integration: past, present, and proposed

The present paper provides an overview of past, present, and proposed models of differentiated integration (DI) in the European Union. First, it reviews the quantitative and qualitative evidence on the historical use of differentiation from 1958 to 2020, finding that it is a common but relatively secondary feature of European integration and that the three idealtypical models identified in the literature (multi-speed, multi-tier, and multi-menu) are deployed in an eclectic, versatile, and constrained manner, which could be termed ‘reluctant differentiation’. Second, it examines and assesses a sample of 21 reform proposals covering the full range of possibilities for the future development of the EU: from total disintegration to a federal union, from maximum uniformity to sustained differentiation, the use of different differentiation models, and other design elements. It finds that differentiation plays an important role in most proposals and may represent an essential tool to increase their effectiveness, popular support, and legal-political feasibility, even though any radical shift toward a more differentiated Europe is unlikely to be implemented.