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, dependent territories, and special areas of geographical interest. It defines three sets of country codes:
ISO 3166-2, Codes for the representation of names of countries and their subdivisions – Part 2: Country subdivision code, defines codes for the names of the principal subdivisions (e.g., provinces, states, departments, regions) of all countries coded in ISO 3166-1.
ISO 3166-3, Codes for the representation of names of countries and their subdivisions – Part 3: Code for formerly used names of countries, defines codes for country names which have been deleted from ISO 3166-1 since its first publication in 1974.
The first edition of ISO 3166, which included only alphabetic country codes, was published in 1974. The second edition, published in 1981, also included numeric country codes, with the third and fourth editions published in 1988 and 1993 respectively. The fifth edition, published between 1997 and 1999, was expanded into three parts to include codes for subdivisions and former countries.
The ISO 3166 standard is maintained by the ISO 3166 Maintenance Agency (ISO 3166/MA), located at the ISO central office in Geneva. Originally it was located at the Deutsches Institut für Normung (DIN) in Berlin. Its principal tasks are:
To add and to eliminate country names and to assign code elements to them;
To publish lists of country names and code elements;
To maintain a reference list of all country code elements and subdivision code elements used and their period of use;
To issue newsletters announcing changes to the code tables;
The ISO 3166/MA has further associated members who do not participate in the votes but who, through their expertise, have significant influence on the decision-taking procedure in the maintenance agency.
Country codes beginning with "X" are used for private custom use (reserved), never for official codes. Despite the words “private custom”, the use may include other public standards. Examples:
The ISO 3166-based NATOcountry codes (STANAG 1059, 9th edition) use "X" codes for imaginary exercise countries ranging from XXB for "Brownland" to XXY for "Yellowland", as well as for major commands such as XXE for SHAPE or XXS for SACLANT.