The ne bis in idem principle (procedural defence) proscribes multiple criminal proceedings and punishments for the same criminal offence/conduct, which is predicated on a final verdict of acquittal or conviction by a court of competent jurisdiction. Incorporated as a fundamental human right through Article 4 of Protocol No. 7 annexed to the ECHR and fundamental right safeguarded through Article 50 CFR, the principle is conjoined with the right to free movement of persons through Article 54 CISA. An evaluation of the characteristics, substance, rationale, scope, and limitations associated with the autonomous procedural defence reveals corresponding purposes. CJEU and ECtHR jurisprudence have delineated the scope and limitations of the procedural defence and the two European courts have reciprocally influenced their respective case law. Definitive and practical judicial guidelines on the application of the principle facilitate consistency of approach by diverse national legal systems consistent with the principle of legality.

The ne bis in idem principle is one of the most fundamental guarantees in criminal procedure law. It prohibits a second prosecution in cases that have already been concluded by a final decision. According to the traditional understanding, the principle excludes a duplication of proceedings only within the same jurisdiction. Art. 50 CFR, however, which was incorporated into primary EU law by Art. 6 TEU, extends the principle’s scope to the transnational sphere to the effect that a final decision in one Member State constitutes a bar to new proceedings in other Member States of the EU as well. While this transnational ne bis in idem guarantee in principle allows for limitations, these must meet the requirements provided for by Art. 52 para. 1 CFR.