The thesis examines whether international organizations may confer their "nationality" on means of transportation. It focuses on intergovernmental organizations but also examines the position of other non-territorial subjects. Ships, aircraft and space objects are covered. The study investigates the concept of nationality of means of transportation and examines the rules on conferral of nationality (resgistration) that developed for States. It then looks for express customary or conventional rules that enable, or forbid, international organizations to register objects. An answer is found in space law only. The thesis then moves to the internal legal order of international organizations, investigating whether constituent instruments expressly contain the right to register, and whether such right can arise as an implied power. In the last part, the thesis designs a legal regime of objects internationally registered, and distinguishes it from the regime applicable to objects that perform an official mission for international organizations