The research project "Differentiated Integration in Europe" is jointly conducted by the Chair of European Politics at the ETH Zurich and the Chair of International Relations and Conflict Management at the University of Konstanz and jointly funded by the Swiss National Science Foundation (SNF) and the German Research Foundation (DFG). The project aims at detecting instances of differentiated integration (DI), such as opt-outs and opt-ins, in the bodies of primary and secondary EU law, at compiling a comprehensive DI dataset covering the period 1958-2011 and at describing and explaining the extent of DI at the system, country and policy level using rational-intergovernmentalist, constructivist and institutionalist theories, on the one hand, and quantitative methods of the social sciences, on the other.
- Holzinger, Katharina and Frank Schimmelfennig. 2012. Differentiated Integration in the European Union. Many Concepts, Sparse Theory, Few Data. Journal of European Public Policy 19(2), 292-305.
- Leuffen, Dirk, Berthold Rittberger, and Frank Schimmelfennig. 2013. Differentiated Integration. Explaining Variation in the European Union. Basingstoke: Palgrave.
- Rittberger, Berthold, Dirk Leuffen and Frank Schimmelfennig. Differentiated Integration of Core State Powers. Forthcoming. In: Genschel, Philipp and Markus Jachtenfuchs (eds.) Beyond the Regulatory Polity? The European Integration of Core State Powers. Oxford University Press.
- Schimmelfennig, Frank. Forthcoming. The Euro-crisis and Differentiated Integration, in: Cramme, Olaf and Sara Hobolt (eds.). Democratic Politics in a European Union under Stress. Oxford University Press.
- Schimmelfennig, Frank and Thomas Winzen. Forthcoming. Patterns of Differentiated Integration in the European Union. Journal of Common Market Studies.