With this special issue and as part of the ELJ's endeavour to foster collaborative research projects on European integration, two of its board members, Jacob Öberg and Valsamis Mitsilegas, threw down a challenge to fellow experts in European criminal law: to reflect on the normative foundations of European criminal law. This challenge first took shape with an online symposium organised by Jacob with the support of Örebro University and gathering together the participants in the ELJ special issue. It continued with an exchange on the topic between Valsamis and Jacob hosted by the EU Law Discussion Group at the University of Oxford. It will conclude, following the publication of the special issue, with a conference organised by Valsamis at the School of Law and Social Justice at the University of Liverpool. We hope, nevertheless, that such a challenge will emulate further research and publications on the meaning of European integration through law in other specific fields of EU law as well as transversally.