The European Union is increasingly engaged in criminal justice. In cross-border criminal cases, the decision on which state will commence investigations and bring cases to trial (choice of forum) is made after horizontal mutual consultation and/or with the help of European institutions, agencies and networks. At present, there is no clear framework for choice of forum. Law enforcement agencies consequently enjoy a great deal of discretion. This may lead to negative conflicts of jurisdiction in which no Member State takes action. It may also adversely affect the principle of mutual recognition and facilitate forum shopping, by defendants and/or state authorities. This book aims to help define the interests at stake and to establish the legal parameters within which choice of forum should take place, thus contributing to the further development of this fascinating area of law.