Summary In July 2023, Jichikenkyu published a case note by Professor Yumiko Nakanishi at the Graduate School of Law titled "The principle of ne bis in idem and mutual trust in the European Union." This case note deals with the Kowwowski case (C-486/14), which was decided in 2016. The case concerned the application of the principle of ne bis in idem, which is seen as one of the key principles in criminal law. The principle of ne bis in idem is also found in Japanese law, but in the EU, it is applied not to a single country but to all EU member states. The Court of Justice of the European Union has struck a balance between the principle of ne bis in idem and mutual trust.