With the entry into force of the Treaty of Lisbon, the EU has gained new competences in the field of criminal law. Whereas in the past the focus was on cooperation in criminal matters, the Treaty of the Functioning of the European Union (TFEU) now provides for measures to approximate national legal rules on criminal liability. In addition, it even contains a mandate to establish a European Public Prosecutor’s Office (EPPO). This raises the question whether and how the substantive criminal law of the European Union should be developed, both in the field of legislation to be implemented by the Member States, as well as for the Union itself to serve the functioning of the EPPO.