The criminal justice system, either procedure or substantive, is exposed to more frequent amendments due to the European Law. The rules and Case Law issued by the European Union as well as the European Convention on Human Rights set forth specific obligations of compliance for either the legislator or the local courts, who are required to cope with “multilevel” and interconnected sources of law, which determine that the criminal issue is highly changeable. It is stunning the multiplicity of the instruments involved thereto: from the rules of application of the European Directives for granting the language assistance and information into the criminal trial, to those due to the repeated convictions of the Court of Strasbourg, generating the abolition of the non-appearance and the new – not completely satisfactory – rules of the trial in-absence. The Case Law is even more dynamic, whereby the Constitutional Court plays not only a supplementary role – it is the case of the “European” review and the remedies to the unfair judgment – but even anticipatory – such as the renovation of the preliminary hearing in the appeal – or even alternate, as to the progressive affirmation of the public hearing principle. Without omitting the action of the ordinary courts, keen on insert in the internal legal system some super national dicta – such as the issue of the ne bis in idem and expiration – particularly delicate for the direct incidence on the fundamental principles set forth by the Constitution to the criminal area, especially about the substantive and procedure lawfulness. The aim of this project is analyzing the operability of the obligations of compliance and define the margin of appreciation for the legislator and the national courts, which allow to abide by the indispensable values of our legal system, even in relationship with the obligations executed with the European institutions.