This contribution aims to analyze the integration effect that EU law has had in the criminal law area. In particular, we want to highlight how this happened in the absence of an established (substantive) European Criminal Law, investigating the steps that have upset the cornerstone according to which «the European Union has no competence in criminal law». Indeed, even if the various attempts made to consolidate the foundations of European criminal law (from the Corpus Juris to the European Constitution) have met with failure, EU law has laboriously made its own way even in this matter that has always been reserved for the state monopoly and often governed by a strict principle of legality. This silent movement has posed new challenges for state systems, especially in EU dialogue, accentuating the role of jurisprudence even for those systems that do not know stare decisis. In this regard, we want to focus on the effect, in some ways unexpected, of the punishment widening in criminal matters, deriving from the transposition of EU law, by national legal systems. In conclusion, as an example, we will focus on some issues addressed by the Italian Constitutional jurisprudence aimed to assess the strength of the national criminal system regarding the bursting effects of a bulky, albeit undeclared, European Criminal Law.
