EU criminal law is a controversial area of Union law. It is clear that the founding fathers of the Rome Treaty conceived the Union to primarily constitute an economic space and that the Member States originally had no intention to transfer their sovereignty in the field of criminal law. Despite this, it appears that following the entry into force of the Lisbon Treaty, the Union has gained a specific competence to legislate in criminal matters. There are, however, constraints as to how this power should be exercised. The constraints primarily concern the Union's struggle to overcome the strong sovereignty claims of Member States and the perceived lack of legitimacy on the part of the Union in the field of criminal law.
In terms of legitimacy, it is clear that democratic participation by Union citizens is not self-evident in the shaping of the EU criminal policy. It is therefore essential to analyse how the Union legislator can legitimately exercise a criminal law power if the citizens of the Union do not participate in the legislative procedure. Further, do Union law and the constitutional traditions of the Member States recognise the existence of a democratic principle implying that the European Parliament shall be involved in the adoption of criminal law legislation? And, if so, can the democratic principle constitute grounds for review of EU criminal law legislation?