A country code is a short alphanumeric identification code for countries and dependent areas, primarily used in data processing and communications. Several identification systems have been developed, but the term "country code" frequently refers to ISO 3166-1 alpha-2, which defines short identification codes for most countries and dependent areas. ISO 3166-1 alpha-2 codes are two-letter codes, while ISO 3166-1 alpha-3 codes are three-letter codes, and ISO 3166-1 numeric codes are three-digit codes.
Country codes are also used in the international telephone numbering plan, which is embodied in the E.164 recommendation by the International Telecommunication Union (ITU) . The ITU-T section of the ITU defines county codes in standards E.123 and E.164, and they are dialed before the national telephone number when calling a telephone number in another country. International calls require at least one additional prefix to be dialed before the country code, to connect the call to international circuits, the international call prefix.
For example, the United States country code is +1, which is dialed after the IDD when calling from another country. The United States area code table shows the various city codes for the United States, and United States country codes are followed by these area codes.
