The purpose of this contribution is to provide a comprehensive overview of the situations in which the Charter of Fundamental Rights of the European Union (the ‘Charter’) may apply in the field of criminal law. First, national criminal penalties that seek to enforce substantive EU law ‘implement EU law’ within the meaning of Article 51(1) of the Charter. The same applies to national criminal measures that derogate from the substantive law of the EU. Second, criminal law is no longer foreign to European integration, as parts of that law may be subject to EU legislation. If EU criminal law seeks to facilitate the mutual recognition of judicial decisions by setting a uniform standard of fundamental rights protection, such a standard must comply with the Charter. This shows that both the effectiveness of national criminal laws implementing EU law and that of EU criminal law must be balanced against fundamental rights.