For international commercial disputes, international commercial arbitration and the CISG together can provide a neutral platform. However, it is unclear whether arbitrators are bound by the CISG. This thesis first examines the legal nature of the CISG's application rules, finding that they constitute private international law, which leads to the fundamental matter of whether arbitrators are bound by PIL. International public and European law and legal practice are studied to answer this question, and in the end, a binding nature of PIL in arbitration is rejected. Finally, a cursory look is also taken at the binding effect of substantive law generally in arbitration.