This article describes the approach which the Union Courts have taken in relation to the non bis in idem principle when it concerns dual proceedings by the Commission and National Competition Authorities (NCAs) or by different NCAs. The unity of the legal interest is used by the CJEU as a jurisdictional safeguard for the Commission. Conversely, the identity of the facts determined whether the accounting principle is applicable in dual proceedings. This principle is in dual proceedings by the Commission and an NCA the only applicable expression of the non bis in idem principle. This approach is different from that in other areas of law where Article 50 of the Charter or Article 54 CISA are applied. The application of the non bis in idem principle in the Union’s legal order can therefore be criticized on the basis of lack of unity. It will be argued that these diverging approaches can be aligned without losing the current outcome in competition law cases.