European criminal law consists of EU criminal law and influences stemming from the ECHR regime. The legitimacy of this European criminal law has not really been theoretically examined by criminal law researchers. Many of the previous studies on European criminal law start from the dynamic rationale of general EU law rather than from the thinking which reflects the discipline of criminal law. This work aims to fill this space. The work provides a criminal law-oriented normative view on how the use of European criminal law, and in particular the use of EU criminal law, could be legitimized from the perspective of criminal law doctrine. In other words, the work aims to show how, under which criteria, the use of criminal law as it stands, and the enactment of criminal legislation in particular, can be seen as legitimate. Thus, the aim of this work is not to argue for the legitimacy of criminal law in general. This research suggests that European criminal legislation ought to respect and follow certain European criminalization principles. The research adopts a constitutional approach since the limits for the use of European criminal law, the European criminalization principles, are derived from European constitutional norms. Constitutional elements are also increasingly important to criminal law, especially in its European transnational context.