National Societies can assist their authorities in the development of international humanitarian law (IHL). This role has been consolidated in their mandate, especially through their auxiliary role in support of public authorities in the humanitarian field. This article recalls the main legal bases from which this role is derived. Based on the Belgian Red Cross experience, it demonstrates how the National Societies’ support to the promotion and national implementation measures of IHL can constitute an incentive for further elaboration of IHL treaties and policies. It also highlights their humanitarian diplomacy work to assist the International Committee of the Red Cross's approach at the international level. Finally, the article shares some thoughts to increase the Movement's collective impact in IHL development.
