The entry into force of the Lisbon Treaty poses anew the question of whether, from now on, it will be more likely for the European Union to use this mechanism, or, conversely, the new institutional, jurisdictional and decision-making framework may act as a containment of favourable trends in the development of variable integration formulas. In reality, flexible or differentiated integration instruments, within or outside of the framework of the EU, alongside strictly intergovernmental cooperation between certain EU countries, have existed since the beginning of Community integration.

Flexibility is emerging as a key dynamic of European integration. This shift towards flexibility has major implications. The EU will have to cope with more complexity and less transparency. It also affects the way in which European integration is viewed since it makes a state-like outcome to the process far less likely. Alex Warleigh looks at why flexibility has become such an important feature of the EU. He examines its history, and puts forward a typology to explain the models by which it is understood. He goes on to explore the hazards of flexibility and to look at what it has to offer, arguing that it is best seen as a desirable part of the integration process rather than as a problem. Flexibility, he argues is an important mechanism for the realization of the EU's slogan "unity in diversity".

The European Union (EU) is often portrayed as sacrificing national diversity for European unity. This book explores the alternative of a flexible EU based on differentiated rather than uniform integration. The authors combine normative theory with empirical research on political party actors to assess the desirability and political acceptability of differentiated integration as a means of accommodating heterogeneity in the EU. They examine the circumstances and institutional design needed for flexibility to promote rather than undermine fairness and democracy within and between member states. Clear, balanced, and accessible, the book provides fresh thinking on the future of the EU.

Until the end of the 1990s, EU integration in the area of criminal law centred primarily around the regional deepening of traditional judicial cooperation in criminal matters and the development of law enforcement cooperation (including the setting up of Europol as a support agency). By the end of the 1990s respectively 2000s, the EU also gained (limited) supranational competence in the areas of substantive respectively procedural criminal law. Both judicial and law enforcement cooperation were furthered over the years via the principles of mutual recognition respectively availability, and through the setting up (and development) of Eurojust, the establishment of a European Public Prosecutor’s Office and the further development of Europol. After three decennia, the EU criminal law corpus is impressive – a core component of the EU’s ‘Area of Freedom, Security and Justice’, building on and adding to (both real and presumed) trust between the Member States. No time for stand-still, though. Since 2020, the European Commission has launched a tsunami of new legislative proposals, including in the sphere of EU criminal law, strongly framed in its new EU Security Union Strategy. This special issue on ‘EU criminal policy. Advances and challenges’ discusses and assesses some of the newest developments, both in an overarching fashion and in focused papers, relating to key 2022 novelties for Europol (ie the competence to conduct AI-based pre-analysis in (big) data sets, and extended cooperation with private parties), the sensitive debate since 2020 on criminalising (LGBTIQ) hate speech and hate crime at EU level, the 2022 Cybersecurity Directive, the potential of the 2020 Conditionality Regulation to address rule of law issues undermining the trustworthiness of Member States when issuing European Arrest Warrants, and concerns about free speech limitation by the 2021 Terrorist Content Online Regulation.

The Routledge Handbook of Differentiation in the European Union offers an essential collection of groundbreaking chapters reflecting on the causes and consequences of this complex phenomenon. With contributions from key experts in this subfield of European Studies, it will become a key volume used for those interested in learning the nuts and bolts of differentiation as a mechanism of (dis)integration in the European Union, especially in the light of Brexit. Organised around five key themes, it offers an authoritative "encyclopaedia" of differentiation and addresses questions such as: How can one define differentiation in the European Union in the light of the most recent events? Does differentiation create more challenges or opportunities for the European Union? Is Europe moving away from an "ever closer Union" and heading towards an "ever more differentiated Union", especially as leading political figures across Europe favour the use of differentiation to reconcile divergences between member states? This handbook is essential reading and an authoritative reference for scholars, students, researchers and practitioners involved in, and actively concerned about, research in the study of European integration. As European differentiation is multifaceted and involves a wide range of actors and policies, it will be of further interest to those working on countries and/or in policy areas where differentiation is an increasingly relevant feature. The Introduction and chapters 13, 21, 30, and 35 of this book is available for free in PDF format as Open Access from the individual product page at www.routledge.com. It has been made available under a Creative Commons Attribution-Non Commercial-No Derivatives 4.0 license.

European Integration in the Twenty-First Century provides a comprehensive overview of the many dimensions and challenges to the on-going European integration project. It employs a number of interdisciplinary perspectives to review processes of both unity and disunity providing the reader with a complete snapshot of contemporary European integration in its variety of settings.