Enhanced cooperation in practice. An analysis of differentiated integration in EU secondary law

The article offers a first comprehensive overview of the workings of enhanced cooperation in the European Union (EU). Although this form of secondary law differentiation exists since the Amsterdam Treaty, it has only rarely been used so far. In the article, we formulate a theory of when and why enhanced cooperation is used in EU decision-making. Our theory builds on rationalist institutionalism focussing on institutions, preference constellations and the externality structure of policies. We test the plausibility of our theoretical claims by combining comparative and within-case analyses of nine cases. The empirical findings underline that the usage of enhanced cooperation depends to large degrees on the externality structure of the goods under consideration. The article ends with a short normative evaluation of the enhanced cooperation procedure.