The history of ICAO is closely
connected with the adoption of the Chicago Convention. The Chicago Convention is the main
source of international public air law. Before the
ratification of the Chicago Convention, PICAO was
established by 26 states. It was in effect from June
6, 1945, to April 4, 1947. By March 5, 1947, the
26th ratification was adopted. ICAO was established on April 4, 1947. In October of the same
year, ICAO became a specialized UN agency affiliated with the ECOSOC - Economic and Social
Council.