The International Civil Aviation Organization is an agency in the United Nations. It manages, standardizes, and recommends practices in regards to air transport. It was created in 1944 with the Chicago Convention on International Civil Aviation, establishing the U.N. oversight agency.
It is currently headquartered in Montreal, Canada with it’s head being the Secretary-General Fang Liu of China.
The ICAO is recognized by every country except for Liechtenstein, Dominica, and Tuvalu. Tuvalu is the only country in the world that has an international airport that is not part of the ICAO, meaning the ICAO’s rules and standards are more or less universal.
Note: There are currently ongoing disputes regarding the membership of Taiwan in the ICAO due to pressure from China.