At the Chicago Conference, the drafters of the Convention on International Civil Aviation had anticipated the emergence of a United Nations type of post-war organization. Accordingly, they wrote into the Convention a provision covering the possibility of ICAO becoming a constituent of such organization as follows:
The Organization may, with respect to air matters within its competence directly affecting world security, by vote of the Assembly, enter into appropriate arrangements with any general organization set up by the nations of the world to preserve peace.
At the first ICAO Assembly held in May 1947, Resolution A1-2 was adopted by unanimous vote of the 32 Contracting States represented at the 3rd Plenary Meeting. This approved the agreement of relationship with the United Nations (UN) and authorized the President of the Council to sign a protocol bringing into force the agreement concerning such a relationship between the UN and ICAO.
President Warner signed the protocol on 3 October 1947 and ICAO became a UN specialized agency. By this agreement, each organization undertakes to fulfil certain requirements whereby the other may participate in its work in the measure required for fulfilment of certain articles of the Chicago Convention and the Charter of the UN.
While ICAO remained an independent and autonomous agency, its acquisition of constituency status in the United Nations Organization was a major step, which greatly benefited many of its Contracting States in the years which followed, mainly through the United Nations Programme of Technical Assistance.
As a Specialized Agency of the UN, ICAO works closely with the UN, and particularly with the Economic and Social Council. In light of its technical mandate, ICAO also works closely with other UN Specialized Agencies and International Organizations, such as: