No abstract

Differentiation has become a salient feature of European integration. Yet systematic empirical evidence is lacking about its origins, duration and variation across countries and policies. This article provides such evidence from a new data set on differentiation in European Union treaty law. In addition, it is argued that two logics of treaty-based differentiation are at work. 'Instrumental differentiation' originates in enlargement and is motivated by efficiency and distributional concerns. 'Constitutional differentiation' has its origins in treaty revisions and is motivated by concerns about national sovereignty and identity. It is driven by Eurosceptic Member States that are opposed ideologically, or fear popular resistance, to the supranational centralization of core state powers.

This chapter maps the development of differentiated integration over the entire history of the EU and across all member states and policies. It shows that differentiation has been on the rise in treaty law and legislation. Yet, relative to the dramatic growth in EU authority and member states over time, there is no evidence for a trend towards ‘ever looser union’. This chapter further shows that differentiated integration is mainly ‘multi-speed’. Most national opt-outs are temporary and end after a few years. However, there is evidence for ‘multi-tier’ integration, too. A small and stable periphery has formed driven by Denmark and the United Kingdom. While there is no sign of multi-menu integration, differentiation also has a policy dimension in that the integration and differentiation of core state powers shapes the evolving multi-tier structure of the EU. In contrast, the EU’s market and flanking policies constitute the domain of multi-speed integration.

This article analyses to what extent and why national parliaments have created oversight institutions to adapt to European integration. Employing data from 22 member states from 1984-2006, the analysis suggests that government-supporting parliamentary groups create oversight institutions to enhance policy participation as integration becomes more important. Moreover, parliamentarians improve their access to information about government policy if governing parties are internally divided over European integration. Finally, oversight institutions that constrain the government's discretion to act in European Union affairs exist in Eurosceptic countries, where they help parliamentarians to enhance electoral security.

Differentiated integration in the European Union (EU) has been primarily discussed and analyzed at the treaty level, whereas lack of systematic data has hampered the examination of secondary-law or legislative differentiation. We present a new data set of differentiation in EU legislation from 1958-2012, a descriptive analysis, and a comparison of the patterns of primary and secondary-law differentiation across time, member states, and policies. We find that differentiation facilitating the accession of new members and constitutional differentiation accommodating the opposition against the integration of core state powers drive both primary and secondary law differentiation. In addition, we find complementarity between differentiation in treaty law and secondary legislation depending on the availability and salience of differentiation opportunities.

International parliamentary institutions (IPIs) have become an established feature of international politics. While scholars of international institutions have extensively studied why states delegate to international organizations (IOs) in general, they have said little about the creation of parliamentary bodies. Moreover, IPIs do not fit the functions commonly attributed to international delegation. By differentiating between general-purpose and taskspecific IOs, we hypothesize that general-purpose IOs establish and maintain parliamentary bodies that serve their legitimation needs. A nested quantitative and qualitative analysis based on an original dataset on the emergence of IPIs and case studies on the reform of the Economic Community of West African States and the development of the Pacific Islands Forum supports this explanation.

The literature suggests that legislative politics among European Union Member States is characterised by economic exchanges, and constrained by the social norms of a European community of legislators. Both views draw a clear line between the legislative process and the conflicts over sovereignty that have left their mark on treaty making and European public opinion since the 1990s. This article suggests revisiting this view, based on an analysis of why Member States have opted out of legislation from the 1970s to today. It argues that differentiation, while once a response to capacity problems of relatively poor countries, has recently become driven by sovereignty concerns of the Union's wealthy and nationally oriented Members that oppose the EU's intrusion into core state powers. The article presents evidence for the impact on legislative outcomes of factors so far thought not to matter. The results indicate greater European‐level legislative responsiveness towards national sovereignty demands than previously recognised. They underline that the nature of European politics has been changing with the EU's push into core state powers.

Existing research on the European Union's (EU) multilevel parliamentary system builds on the hypothesis of parallel evolution, situating explanations for European Parliament (EP) empowerment at the EU level and explanations for national parliamentary powers in EU affairs at the national level. We propose the hypothesis of co-evolution, which specifies a connection between national and European arenas of parliamentarization. We study whether the EP's empowerment enhances or reduces pressure on national parliaments to strengthen their own EUrelated competences. First, we argue that national parliamentary parties take conscious positions on the powers of the EP. Second, support for the EP among the party composition of national parliaments tells us whether parliaments regard the EP as a competitor or ally, feeling pressed, or relieved of the pressure, to strengthen their EU-related competences.