This article examines the evolution of EU counter-terrorism cooperation since 2001. It considers the extent to which it has become more supranational over time and identifies the main factors accounting for this evolution. In order to do so, it begins by locating ‘supranationalism’ as the end point of a continuum that has ‘intergovernmentalism’ as the other end point. Drawing and critically reflecting upon the literature on supranationalism and the Community method, it identifies a series of criteria according to which various stages in the development of a given policy can be placed on this continuum. Those are then adapted to the specific case of the EU counter-terrorism policy. This analytical framework is subsequently applied to the main periods in the development of EU counter-terrorism cooperation, namely the origins in the aftermath of 9/11, the response to the Madrid and London terrorist attacks, the 2006-2013 period, the response to the challenge of the foreign terrorist fighters, and the post-Daesh period. The article shows that the supranational characteristics of EU counter-terrorism cooperation have gradually been reinforced.

The article outlines the literature on analysing European integration in the AFSJ, highlights the theoretical framework for the special issue, and underlines the main contributions of the collection of articles to the existing literature. It emphasises the paradox of integration in the ASFJ: substantial integration, driven by the EU institutions, has taken place, embracing new substantive areas, actors and governance methods, despite the policy area entailing high sovereignty and national identity costs for the Member States. It argues that integration in the AFSJ should most appropriately be studied along the intergovernmental-supranational spectrum, juxtaposing the intergovernmental emphasis on state and government control against the supranational vision and reliance on the framework of ‘integration through law’. Through a reconceptualised notion of supranationalism that goes beyond the ‘Community’ method, it suggests a novel research direction for the policy area by testing the hypothesis that dominant accounts in the field have underappreciated the role of law in shaping the distinctive trajectory of European integration over time. It proposes that the contributions of the special issue highlight this through both general theoretical analyses of law and policymaking in this area and, on the whole, specific case studies of distinctive sub-policy fields in migration, asylum, criminal justice, policing, and counterterrorism, which show stronger supranational governance in the AFSJ.

What to make of the paradox that the area of freedom, security and justice is characterized both by high levels of legal supranationalisation and by arrangements marked by little law? This paper argues this is because the EU takes a dominant position in the government of migration and international protection, on the one hand, and these fields are amongst the most politically fissile of our time, on the other. To govern them, therefore, stretches the EU’s institutional, affective, and regulatory resources. This has led to three responses. The first is high EU legalization and expansion of regulatory capacity: more comprehensive and intensive EU law intervention, active engagement by the ECJ and national courts, and agency development. This struggles with the extent of governmental demands. The second response is, therefore, resort to Mark I Shadows, non-legal arrangements developed in highly legalised areas where EU law is perceived as unable to meet the expectations of EU government, and which act as a substitute for EU law. The third is Mark II Shadows, which involve both an active aversion to EU law and occur most frequently when the EU does not have the tools to govern and must rely on coopting the resources of others. These Mark II Shadows move EU government to a new paradigm of ‘integration without law’.

This article examines the evolution of interoperability within the European Union’s counterterrorism policy framework, arguing that recent developments represent a paradigmatic shift rather than incremental institutional change. Drawing on historical and constructivist institutionalism, we contrast the limited policy outcomes following the Madrid (2004) and London (2005) terrorist attacks with the ongoing implementation of a centralized EU interoperability framework since the Paris (2015) and Brussels (2016) attacks. Utilizing empirical data from EU documents and expert interviews, we identify cognitive reframing, strategic policy entrepreneurship, and positive feedback mechanisms as drivers of this transformation. Our findings suggest that while the interoperability agenda promises to enhance cross-border security coordination, it also raises critical concerns regarding data protection and purpose limitation. As such, interoperability illustrates both the potential and the tension of EU internal security integration: it offers functional gains in counterterrorism governance, but also reveals the normative and operational challenges of embedding supranational data infrastructures in a fragmented political and legal environment.