The first two freedoms concern the passage of commercial aircraft through foreign airspace and airports, while the other freedoms concern the international transport of people, mail and cargo. The first to the fifth freedoms are officially listed by international treaties, especially the Chicago Convention. Several other freedoms have been added and, although most are not officially recognized in international treaties of general application, they have been agreed by a number of countries. The freedoms cited in lower numbers are relatively universal, while the higher numbers are rarer and more controversial. Open-air liberal agreements are often the least restrictive form of air agreements and can encompass many, if not all, freedoms. They are relatively rare, but recent single air transport markets in the European Union (European Aviation Area) and between Australia and New Zealand are examples. The Open Skies policy covers nine air freedoms, as defined under the International Civil Aviation Convention (also the Chicago Convention), signed in Chicago in 1944. The freedoms are as follows, cited by the International Civil Aviation Organization (ICAO), the body that established and governs the Chicago Convention.  After the consolidation of small airlines in the Central American subregion in the early 1990s, other separate but almost identical open skies agreements were concluded with the United States in 1997.
By 1995, the U.S.-Canada Air Services Agreement had already entered into force, primarily based on the “open skies” model. In South America and the Caribbean, regional liberalization initiatives led to the liberalization of air transport between 1991 and 1999 with a view to the adoption of agreements of the Andean Community (CAN), the Caribbean Community (CARICOM) and the Southern Common Market (MECROSUR); Caribbean States Association (ACS) Air Navigation Agreement in 2008. All of these initiatives are aimed at harmonizing aviation policy and liberalizing the granting of transportation rights and market access.