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.