This article analyses why the UN’s members delegate resources to the UN Secretariat in the sensitive field of peacekeeping. It argues that the Secretariat can carry out planning and implementation functions more efficiently, but that the states remain wary of potential sovereignty loss. Through a mixed methods approach, this article provides evidence for such a functional logic of delegation, but shows that it only applies from the late-1990s on. The change in approach of states towards delegation can be explained by feedback from the dramatic failures of peacekeeping in Bosnia and Herzegovina, Rwanda and Somalia.