EU Criminal Law is perhaps the fastest-growing area of EU law. It is also one of the most contested fields of EU action, covering measures which have a significant impact on the protection of fundamental rights and the relationship between the individual and the State, while at the same time presenting a challenge to State sovereignty in the field and potentially reconfiguring significantly the relationship between Member States and the EU. The book will examine in detail the main aspects of EU criminal law, in the light of these constitutional challenges. These include: the history and institutions of EU criminal law (including the evolution of the third pillar and its relationship with EC law); harmonisation in criminal law and procedure (with emphasis on competence questions); mutual recognition in criminal matters (including the operation of the European Arrest Warrant) and accompanying measures; action by EU bodies facilitating police and judicial co-operation in criminal matters (such as Europol, Eurojust and OLAF); the collection and exchange of personal data, in particular via EU databases and co-operation between law enforcement authorities; and the external dimension of EU action in criminal matters, including EU-US counter-terrorism co-operation. The analysis is forward-looking, taking into account the potential impact of the Lisbon Treaty on EU criminal law.