By 1945, states both near and far were increasingly linked by privatized air transport, prompting officials with the still Provisional International Civil Aviation Organization (PICAO) to take a more localized approach to solving the range of problems facing worldwide civil aviation.

To accomplish this, States worked through the PICAO to divide the world into 10 air navigation regions in late 1945. Regional Route Service Organizations (RRSO) were then established during two key meetings, the first Session of the Committee on Air Navigation (2 October 1945 to 27 November 1945) and the second Session of the Interim Council (15 October to 30 November 1945). Comprised of technical experts and state representatives, the RRSOs studied, interpreted and customized international standards and practices for their geographical area while planning special cooperative measures for air navigation facilities around the world.

The 10 original RRSOs included the North Atlantic, European-Mediterranean, Middle East, Caribbean, South East Asia, South Atlantic, South Pacific, North Pacific, South America and African-Indian Ocean. As many vacated military facilities and air routes transitioned to civilian usage after the war, early coordination actions were an important necessity.

On 4 March 1946, the first regional meeting of the North Atlantic RRSO, held in Dublin, Ireland, addressed the drastic curtailment of military air transport services. This led to a series of regional air navigation meetings, with the second occurring in Paris in 1946. These Regional Route Service Conferences, later called Regional Air Navigation (RAN) meetings, would be held in each separate region or in areas that covered multiple regions. The RAN meetings continued regularly until November 1953.

Regional offices were usually established subsequent to a RAN meeting being held, for example in Dublin for the North Atlantic region, Paris for the European-Mediterranean and Cairo for the Middle East. There was also a temporary mission in Melbourne, Australia for the South-West Pacific region.

In May of 1947, the First Assembly of the ICAO convened and it was decided that no more than five regional offices were needed, in order to rationalize the global coordination structure and maximize available efficiencies. By 1951, there were offices located in Cairo, Lima, Melbourne, Montréal and Paris.

Eventually, the number of RRSOs was also reduced, from 10 to eight during the 16th Session of the ICAO Council (15 May to 15 July 1952). This decision merged North and South Pacific regions as well as the South American and South Atlantic.

The Melbourne office moved to Bangkok, Thailand in 1955, and two years later, on 14 February 1957, ICAO’s North American, Central American and Caribbean Regional Office moved to Mexico City.

In 1963, a sixth regional office was established in Dakar, Senegal. Two decades later, in December 1983, the Eastern African Office was opened in Nairobi, Kenya, raising ICAO’s Regional presence to the seven Regional Offices which continue to serve States and global aviation to this day.