In November and December 1944, delegates of 52 nations met at the International Civil Aviation Conference in Chicago to plan for international cooperation in the field of air navigation in the postwar era. It was this conference that framed the constitution of the International Civil Aviation Organization—the Convention on International Civil Aviation, also called the Chicago Convention. This convention stipulated that ICAO would come into being after the convention was ratified by 26 nations. To respond to the immediate needs of civil aviation, a provisional organization was created and functioned for 20 months until, on 4 April 1947, ICAO officially came into existence.