PurposeThe purpose of this article is to compare the methods of interpretation and gap filling in the United Nations Sales Convention (CISG) and in the Draft Common European Sales Law (CESL). In particular, it aims to examine whether the established interpretation and gap filling method of the CISG can and should be used for the CESL.Design/methodology/approachThe article looks at the method by which international case law and doctrine interpret the CISG and fill its gaps. The article compares this method with the method that is provided for in the CESL instrument but has to be implemented.FindingsIt is suggested that despite its nature as European community law, CESL should be interpreted in a broad international way since it does not only cover internal EU sales, but also transactions involving parties from outside the EU. For this reason its interpretation and gap filling should follow the method of the CISG so as to interpret similar provisions in a similar way in order to harmonize law within and outside the EU.Research limitations/implicationsBoth the CISG and CESL intend to unify legal traditions or different legal systems; the CISG tries to harmonize globally what CESL tries to harmonize regionally. It is important that these two instruments complement one another by the avoidance of divergent interpretations of similar provisions. It would helpful for further research to assess whether and how two decades of experience with the CISG can be used in the interpretation and application of CESL.Practical implicationsCESL's interpretation provision, if it is enacted, is unlikely to change from the current version. The way CESL is interpreted and how its gaps filled will determine its practical significance as a viable opt‐in national law. It is therefore necessary to develop in advance the right interpretive methodology if CESL is to become a meaningful alternative instrument.Originality/valueThe article suggests that the CESL should not be interpreted in the traditional way European community law is interpreted, but, instead, be interpreted under a broad international perspective. It also advances the idea of interconventional interpretation by which the CISG would guide the interpretation of similar provisions found in CESL.