ISO 3166-1 is a list of two-letter codes for existing sovereign nations developed by the International Standard Organization (ISO).
The purpose of the ISO 3166 standard is to define internationally recognized codes of letters and/or numbers that are used to refer to countries and subdivisions within those countries. The standard defines multiple codes for specific countries, including codes used for historical purposes. For example, SU, once the code for Soviet Union, has been removed to the ISO 3166-1 list and placed on the ISO 3166-3 list with a new four-letter code, SUHH, to indicate that the Soviet Union no longer exists as a country, and was not replaced by a different sovereign entity.<https://www.iso.org/obp/ui/#iso:code:3166:SU ISO Online Browsing Platform - SU]</ref> The code ZR, for "Zaire," was removed from the ISO 3166-1 list and placed on the ISO 3166-3 list as ZRCD, indicating that ZR has become CD, the new ISO 3166-1 code for the Democratic Republic of the Congo.
ISO 3166-1 and ccTLDs
The ISO 3166-1 Alpha-two code was adopted by RFC 1591 as the two-letter ccTLD, delegable to each country's ccTLD registry operator. RFC 1591 enshrines a core premise of IANA functions as they relate to ccTLDs - "The IANA is not in the business of deciding what is and what is not a country." The ISO 3166-1 list is used because it is maintained by a neutral body that undertakes regular review of the list, and has explicit and transparent standards for decision-making regarding changes to the list.
ICANN has not yet adopted a consistent policy for dealing with delegated ccTLDs whose countries "cease to exist," at least in the view of the ISO 3166 Maintenance Agency. A PDP for retirement of ccTLDs is in the final stages of public comment and consideration by the ICANN Board.
Similarly, there is currently no policy for dealing with approved and delegated internationalized country code top-level domains when the related country code is removed from or amended on the ISO-3166 standard. The ccNSO is also engaged in a policy development process to fill that gap in policy, as well as to provide additional structure and rules for managing variant strings of the same country name.