Telephone country code

A telephone country code is a country-specific telephone number prefix for international direct dialing (IDD), a system for reaching telephone service subscribers in foreign areas via international telecommunication networks. Country codes are defined by the International Telecommunication Union (ITU) in ITU-T standards E.123 and E.164.

Country codes constitute the international telephone numbering plan. They are used only when dialing a telephone number in a foreign region other than the caller's. They are dialed before the national telephone number. Typically, the intend of dialing a foreign telephone number, requires at least one additional prefix, the international call prefix which is an exit code from the national numbering plan to the international one. It essentially requests and reserves an international telephone circuit for the call. ITU standards recommend the digit sequence 00 for this prefix and most countries comply. The prefix is 011 in the countries of the North American Numbering Plan (NANP), while a minority of countries use other prefixes. When printing telephone numbers the requirement of dialing this prefix is indicated by a plus-sign (+) in front of a complete international telephone number, per ITU Recommendation E164.

Country codes were originally introduced and termed International Codes in 1960 by the International Telegraph and Telephone Consultative Committee (C.C.I.T.T.) in the II^nd Plenary Assembly in New Delhi,^[1] but have sometimes also been referred to as "country dial-in codes", or historically as "international subscriber dialing" (ISD) codes in the United Kingdom.

A country or region with an autonomous telephone administration must apply for membership in the International Telecommunication Union (ITU) to participate in the international public switched telephone network (PSTN). Country codes are defined by the ITU-T section of the ITU in standards E.123 and E.164.