countrycode

Country code refers to a short code that identifies a country or dependent territory in a variety of international contexts. The most widely used standard is ISO 3166, which defines two-letter codes (alpha-2) and three-letter codes (alpha-3), as well as numeric codes. These codes appear in data schemas, databases, shipping labels, software localization, and domain labeling. ISO 3166-1 alpha-2 codes are particularly common in internet domains and programming locales, while alpha-3 codes provide an unambiguous textual form. The ISO 3166 Maintenance Agency oversees updates as geopolitical statuses change.

Other systems assign country identifiers for specific purposes. In telecommunications, ITU-T E.164 specifies country calling codes used to route international phone numbers, such as +1 for the United States and Canada, and +44 for the United Kingdom. In the internet infrastructure, country code top-level domains (ccTLDs) map largely to ISO alpha-2 codes, for example .us for the United States. The United Kingdom uses the ccTLD .uk, even though its ISO alpha-2 code is GB, illustrating that ccTLD assignments are not always a direct one-to-one with ISO codes.

Examples help illustrate the mapping. The United States has ISO alpha-2 code US, alpha-3 USA, ccTLD .us, and calling code +1. The United Kingdom has ISO alpha-2 code GB, alpha-3 GBR, ccTLD .uk, and calling code +44.

See also: ISO 3166, ITU-T E.164, ccTLDs, locale identifiers.