Conduct and subsequent practice by states in the application of the requirement to report under UN Charter Article 51

United Nations Charter Article 51 obliges states to immediately report the use of self-defence to the United Nations Security Council (UNSC). Besides the wording in Article 51, there are no (codified) rules or guidelines on how states should report or what should be included in the report to the UNSC. Reporting on self-defence is predominantly based on the conduct of UN member states and how these actors interpret their obligations. This article analyses whether there is common conduct that could indicate subsequent practice by parties to the Charter regarding the format of reporting, the notion of immediacy in reporting and the quality of reports submitted to the UNSC. It was found that there is subsequent practice identifiable regarding the format of reporting, that there are reliable indicators on parallel conduct regarding the immediacy of reporting and common conduct when reporting on measures taken in self-defence.