The Chicago Convention (also known as the Convention on International Civil Aviation), established the International Civil Aviation Organisation (ICAO), a specialized agency of the United Nations charged with coordinating and regulating international air travel. The Convention establishes rules of airspace, aircraft registration and safety, and details the rights of the signatories in relation to air travel; it also exempts air fuels from tax. The Convention was signed by 52 states on 7 December 1944 in Chicago, Illinois, U.S., and came into effect on 4 April 1947.
The Convention provided for the sovereignty of airspace above the territory of each state, together with five freedoms (later expanded to nine by the addition of four unofficial freedoms) which govern the freedom of states to operate air transport flights (including the carriage of passengers, cargo and mail) across, into and within the airspace of other states. Only the first two of these freedoms (see below) apply automatically to signatory states, the remainder being subject to national agreement.