A Contracting State of ICAO is a State which has adhered to the Chicago Convention on International Civil Aviation, whether or not it is a member of the United Nations (UN) and/or any of its other Agencies, e.g. Switzerland. A non-Contracting State of ICAO, on the other hand, is a State which has not signed and does not adhere to the Chicago Convention, but which is a member of the UN and/or any of its other Agencies, e g. the Holy See. There is a third category: that of States which are not signatories to the Convention on International Civil Aviation and which are not members of the United Nations nor of any of its Agencies. Very few States belong to this category, which has not been given a specific name.
For purposes of planning and facilitating the follow-up of implementation of the required air navigation services and facilities, States have been categorized into two main groups: those which are geographically situated within the region or have territory in that region, and those which are not located in the region but have air carriers on their registry which conduct international air traffic operations in the region. The States belonging to the first group are essentially those which are responsible for the provision of the services and facilities required in the region and are, for purposes of brevity, referred to as 'provider' States. The States of the second group are usually referred to as 'user' States.
Under the foregoing groupings, a State may be both a 'provider' and a 'user' State in the region in which it is situated or in other regions in which it has territories. A State may also have provider interests in a number of regions due to its location in an area where the various air route networks associated with the regions overlap. An example of this is the United States which has provider interests in the Pacific, the North Atlantic, the Caribbean and the North American Regions. On the other hand, a State may have user interests in any number or all of the established air navigation regions depending on the international routes flown by its airlines. Examples are France, Japan, the United Kingdom, the United States, etc., whose airlines operate globally.