ISO 3166 is a standard published by the International Organization for Standardization (ISO). It is used to code the names of countries, autonomous regions, provinces and states. The official name of the standard is Codes for the representation of names of countries and their subdivisions. It consists of three parts:
- ISO 3166-1, Codes for the representation of names of countries and their subdivisions – Part 1: Country codes, defines codes for the names of countries, autonomous regions, provinces and states. It defines three sets of country codes:
- ISO 3166-1 alpha-2 – two-letter country codes, used prominently in internet country domain codes with a few exceptions (e.g. TR for Türkiye)
- ISO 3166-1 alpha-3 – three-letter country codes (e.g. TUR for Türkiye)
- ISO 3166-1 numeric – three-digit country codes (e.g. 792 for Türkiye)
- ISO 3166-2, Codes for the representation of names of countries and their subdivisions – Part 2: Country subdivision code, defines codes for the subdivisions (provinces, states, etc.) of the countries defined in ISO 3166-1 (e.g. TR-34 for Istanbul)
- ISO 3166-3, Codes for the representation of names of countries and their subdivisions – Part 3: Code for formerly used names of countries, defines the names of countries that have changed their names or no longer exist since ISO 3166-1 was first published (1974) (e.g. SUHH for the Union of Soviet Socialist Republics)
