One of the most dynamic areas of EU law since the great changes brought to the EU constitutional order by the Amsterdam Treaty in 1999 has been cooperation in the fields of policing and criminal justice. Both fields have already been the subject of substantial legislative effort in the EU and an increasing amount of judicial activity in the European Court of Justice. In 2007 - after the Constitutional Treaty of 2004 failed - the new Reform Treaty planned very substantive changes to these policies. Bringing together a wide-ranging set of topics and contributors, this book enables readers to understand these changes by examining three key questions: how did we get to the Reform Treaty; what have been - and still are - the key struggles in competence; and how do the changes fit into the transformation of police and judicial cooperation in criminal matters in the EU?