Which international treaty governs the use of airspace?

The Chicago Convention, formally known as the Convention on International Civil Aviation, was established in 1944 and is the foundational treaty governing international air navigation. It laid down the principles for the regulation of international air transport and established the International Civil Aviation Organization (ICAO), which is responsible for promoting the safe and orderly development of international civil aviation.

Among its many provisions, the Chicago Convention stipulates that a state has complete and exclusive sovereignty over the airspace above its territory, a key tenet in airspace governance. This sovereignty means that no foreign aircraft can enter a state's airspace without its permission, establishing a clear framework for how nations interact regarding their respective airspaces.

The other treaties mentioned serve different purposes: the Montréal Protocol primarily deals with the protection of civil aviation against acts of unlawful interference, the Vienna Convention focuses on diplomatic relations and treaties between countries, and the Geneva Agreement generally pertains to humanitarian issues in conflict and does not apply to aviation specifically. Thus, the Chicago Convention is rightly recognized as the governing treaty for international airspace usage.