New Monograph on Immunity from Enforcement of States and International Organizations
Victor Grandaubert, who is a lecturer at Paris Nanterre University, has published L’immunité d’exécution de l’Etat étranger et des organisations internationales en droit international (The Immunity from Enforcement of Foreign States and International Organisations in International Law) with the French publisher Pedone in 2023.
The book is based on the doctoral thesis of the author. The main claim is that immunity from enforcement should be considered as functional. The author submits that immunity from enforcement serves the function of enabling States and international organizations to act in the public interest on the territory of the host State, and that immunity from enforcement should therefore be understood as protecting its beneficiary for the purpose of exercising this function. As both foreign States and international organisations are public institutions acting in the public interest on the territory of a State which has exclusive jurisdiction to enforce, they both need the same protection, in order to conduct their public activities on the territory of the host State.
As far as immunities of States are concerned, the main claim requires, as a preliminary step, to challenge the traditional view that immunities of States are founded in the principles of sovereignty and of sovereign equality of States. Dr. Grandaubert argues that this rationale is unable to explain the evolution of the law of State immunities from absolute to limited immunity, and should thus be reconsidered.
Another claim of the book is that, as a result of the main claim, immunities from enforcement of States and of international organizations should not be considered as distinct conceptually, but rather as a single concept benefitting different actors of the international legal order, namely States and international organizations.
The blurb reads:
Pour quelle raison les immunités d’exécution de l’État étranger et des organisations internationales résistent-elles fermement au processus d’érosion des immunités internationales ? Selon toute apparence, contrairement à l’immunité de juridiction, l’immunité d’exécution fait échapper ses bénéficiaires à des actes d’une certaine gravité sur leurs biens, à savoir des mesures de contrainte étatique. Ce constat en soi est toutefois insusceptible d’expliquer la solidité commune dont ces immunités font preuve dans un contexte où l’on distingue a priori entre l’immunité souveraine de l’État et les immunités fonctionnelles des organisations internationales.
Pour appréhender précisément la singularité de l’immunité d’exécution, cette thèse démontre que cette immunité tire sa force de son caractère fondamental pour le maintien de l’architecture du droit international. Il n’en demeure pas moins qu’en analysant ainsi l’immunité d’exécution, la thèse contribue à mettre en évidence l’effacement de la distinction communément admise entre les immunités de l’État et celles des organisations internationales.
En effet, l’immunité d’exécution a par essence pour objet d’assurer une protection contre la contrainte étatique, exercée dans un cadre juridictionnel ou non, aux biens employés par des entités agissant librement en qualité de pouvoir public en dehors d’un cadre exclusivement national. Reflet de la stabilité qui caractérise cette immunité en droit international, la protection qu’elle assure en pratique s’inscrit du reste dans un phénomène de consolidation.
More details can be found here.

I agree that both concepts serve similar functions in public international law. However there is a fundamental difference between both concepts: Immunity of states is a concept of customary international law, as the ICJ stated in several judgments, especiall in Germany vs. Italy (2012). However, the immunity of International Organizations is derived from their foundational treaties and the seat agreements with the hosting state of the organization. Thus, the extent of the immunity of International Organizations is primarily a matter of treaty interpretation. Furthermore, non-contracting states are not bound by the immunity of the International Organisation as there is no protection under customary international law. This lack of protection is a big impediment to the activities of regional international organisations in third states.
I assume that Mr. Grandaubert highlights this issue in his monograph, too. I am curious to read the book.