European Union, and criminal, laws had been interacting in many ways even before explicit competence in criminal matters was acquired by the Union in the Treaty of Maastricht. Such intersections between supranational and national provisions have frequently been handled by the CJEU. In the main, the intervention of the Court is triggered by Member States’ recourse to penal sanctions in situations covered by EU law. In such cases, the CJEU is called upon to strike a complicated balance: it has to deal with Member States’ claims of competence in criminal law, whilst ensuring that that power is used consistently with EU law. By making reference to selected cases, this paper highlights the impact that principles established in the context of the fundamental freedoms can have on EU criminal law.