The influence of EU law on French criminal law is twofold: it first has an impact on substantive criminal law but also on procedural law. The Europeanisation of material criminal law has been rather limited in France in comparison to its influence on procedural criminal law, which has been far more substantial and has destabilised the national criminal-law enforcement area. Europeanisation has had varied consequences: as regards substantive criminal law, it has mainly enhanced the effectiveness of the fight against serious and cross-border crime. By approximating criminal laws, the EU has thus contributed to a hardening of certain criminal sanctions by setting a minimum common core. The Europeanisation of procedural criminal law itself results in a strengthening of the requirement for legitimacy, as the EU strives to better protect fundamental rights by imposing a common standard. According to D. Simon, gone are the days when it seemed incongruous to raise the question of Community competence in criminal justice matters. Criminal law, an area at the very core of national sovereignty, was long regarded as immune to the process of Europeanisation that British magistrate Lord Denning described it as “an incoming tide flowing up the estuaries of England.” Criminal law is, however, subject to the influence of this incoming tide; its Europeanisation leads to some extent to a sharing of sovereignty or maybe, rather, to a duplication of criminal sovereignty. We are witnessing the emergence of a European criminal justice area that is superimposed on the territories of the Member States of the European Union (EU) just as European citizenship is superimposed on the nationality of a Member State. According to E. Gindre, the notion of area implies the flexibility that characterises EU criminal law and that has the merit of not offending the sensibilities of Member States in the essential expression of their sovereignty, particularly their criminal justice sovereignty. There is, after all, an “EU law enforcement system” that results from a progressive Europeanisation of criminal law. Europeanisation is a process whereby criminal law becomes European. This Europeanisation can be viewed in two ways: from a State perspective, by showing that national criminal law is influenced by European legislation, and from a European perspective, by addressing the emergence of a body of European criminal law resulting from European integration. While the concept of Europeanisation has received greater attention in political science than in legal research, some important research has nonetheless already been carried out in the area. According to C. Verdure, Europeanisation in the legal area reflects European integration and the influence of EU law on national laws, which some have called “European naturalisation”. One must take into consideration the interactions between the EU and Member States, without neglecting the dual nature of Europeanisation. Indeed, the “top-down” process whereby national law becomes Europeanised is supplemented by a “bottom-up” process: regulations are adopted at the European level to address national concerns, thanks to a form of “State lobbying”. The approach chosen here is limited in several respects. First, we focus on the “top-down” approach and emphasise the influence of the EU on national (French) criminal law, leaving aside the “bottom-up” aspect of European law integrating national concerns. Furthermore, we analyse Europeanisation through the State prism, noting the effects of European construction on national criminal law without pursuing the result of this Europeanisation as such, the emergence of a body of European criminal law. Finally, the notion of Europeanisation is restrictive to the extent that our study is limited to the EU, even though the Council of Europe and especially the jurisprudence of the European Court of Human Rights (ECHR) have significant influence on criminal procedure in France. While our view may be restrictive as regards the concept of Europeanisation, it is broad as to our definition of criminal law, which includes not only substantive, but also procedural criminal law. We consider all three aspects of the right to punish: incrimination, judgment and sanction. The influence of European construction on French criminal law began very discreetly, substantive criminal law being impacted incidentally at first by Community law. The Maastricht Treaty, by introducing cooperation in the area of justice and home affairs, may have accelerated the process but it was primarily the Amsterdam Treaty#, which set the EU a new goal of establishing an Area of freedom, security and justice (AFSJ), which gradually led to a partial harmonisation of substantive criminal law. The establishment of this area also led to the adoption of a certain number of measures, such as the European arrest warrant (EAW), which influenced French criminal procedure. While under the Amsterdam Treaty the technique of harmonisation was not yet intended to apply to criminal procedure, that step was taken with the Lisbon Treaty, which sets out a specific legal basis for approximating national legislation on certain aspects of procedural criminal law. According to J. Pradel, the Lisbon Treaty thus constitutes a profound “metamorphosis” of the EU in the area of criminal law. Let us dwell for a moment on the various techniques employed by the EU along the way: from cooperation to harmonisation to unification. The first stage of Europeanisation consisted in setting up formal frameworks for cooperation between the police and judicial authorities under the Maastricht Treaty. The Amsterdam Treaty introduced mutual recognition and harmonisation as new, more sophisticated, techniques of Europeanisation. The concept of harmonisation itself refers to two methods that should be distinguished. Harmonisation may, indeed, indicate a simple alignment between two or more legal systems that erases disparities without eliminating national characteristics. It may also be defined as a process whereby different packages of laws are unified through the drafting of a new law that borrows from each. According to J. Pradel, harmonisation complements cooperation. The issue, here, is not to guarantee unified norms for all European States, which would equate to federal criminal legislation. This approach, proposed by the Dutch EU presidency in 2005, was not endorsed by the Council, which considered that unification would challenge the subsidiarity principle and national legal cultures. Harmonisation in the narrower sense of an alignment of legislations allows for a balance between the need for Europeanisation and the preservation of national legal identities, which is so important when it comes to criminal procedure. As Professor Labayle puts it, “Procedural issues reflect a society’s deep-seated balances, whether political, social or historical; it is on these issues that the concessions required for a legal integration process to succeed are most difficult to reach.” The Lisbon Treaty clearly creates new opportunities in criminal matters by explicitly consecrating mutual recognition as the cornerstone of judicial cooperation in criminal matters, since the harmonisation of criminal procedure is a necessary complement. Mutual recognition can be distinguished from instruments of legal assistance inasmuch as it allows foreign criminal decisions to be considered or enforced. This technique has accelerated the process of Europeanisation, because it is much more flexible than harmonisation. Furthermore, the Lisbon Treaty’s consecration of the EU’s criminal jurisdiction has made the harmonisation of criminal law an instrument that is inseparable from the implementation of judicial cooperation. Thus, applying the internal market model, the AFSJ is proving to be an integrating law that aims at approximating national laws to promote free movement. In fact, the influence of EU law on substantive criminal law has been rather limited in France in comparison to its influence on procedural criminal law, which has been far more substantial and has destabilised the national criminal-law enforcement area. It should also be noted that Europeanisation has had varied consequences: as regards substantive criminal law, it has mainly enhanced the effectiveness of the fight against serious and cross-border crime. By approximating criminal laws, the EU has thus contributed to a hardening of certain criminal sanctions by setting a minimum common core. The Europeanisation of procedural criminal law itself results in a strengthening of the requirement for legitimacy, as the EU strives to better protect fundamental rights by imposing a common standard. Thus we will show that substantive criminal law is quietly being Europeanised for the sake of effectiveness (I) while procedural criminal law is being Europeanised more openly, in a spirit of better protection of fundamental rights (II).