Country code top-level domain

A country code top-level domain (ccTLD) is a top-level domain used and reserved for a country or a dependent territory. These are two letters long, and most of them correspond to the ISO 3166-1 standard for country codes.

General information

There are over 243 ccTLDs; see the list of Internet TLDs and IANA's list of ccTLDs. Most ccTLDs correspond to the two-letter ISO 3166-1 country codes, but there are several differences, explained below. Each country appoints managers for its ccTLD and sets the rules for allocating domains. Some countries allow anyone in the world to acquire a domain in their ccTLD, for example Austria (at) and Cocos (Keeling) Islands (cc). Other countries or dependent territories allow only residents to acquire a domain in their ccTLD, for example Canada (ca).

ISO 3166-1 codes not used as ccTLDs

The codes EH and KP, although theoretically available as ccTLDs for Western Sahara and North Korea, have never been assigned and do not exist in DNS. Similarly, the new codes CS (Serbia and Montenegro) and AX (Åland Islands) are not yet assigned as ccTLDs (cs was previously assigned to Czechoslovakia). TL (post-independence East Timor), is now being introduced to replace TP.

All other current ISO 3166-1 codes have been assigned and do exist in DNS. However, some of these are effectively unused. In particular, the ccTLDs for the Norwegian territories Bouvet Island (bv) and Svalbard and Jan Mayen (sj) do exist in DNS, but no subdomains have been assigned, and it is Norid policy not to assign any at present.

Only one domain (dra.hmg.gb, for the Defence Evaluation and Research Agency) is still registered in gb (United Kingdom, although the letters actually stand for Great Britain, a subset of the UK) and no new registrations are being accepted for it. Sites in England, Scotland, Wales and Northern Ireland use uk (see below).

ccTLDs not in ISO 3166-1

Six ccTLDs are currently in use despite not being ISO 3166-1 two-letter codes:

uk (United Kingdom): The ISO 3166-1 code for the United Kingdom is GB, however JANET had already selected uk as a top-level identifier for a pre-existing naming scheme, and this was incorporated into the top-level. gb was assigned with the intention of a transition, but this never occurred and the use of uk is now entrenched.
su (the obsolete ISO 3166-1 code for Soviet Union): The su managers stated in 2001 they will commence accepting new su registrations, but it is unclear whether this action is compatible with ICANN policy.
ac (Ascension Island): This code is a vestige of IANA's decision in 1996 to allow the use of codes reserved in the ISO 3166-1 alpha-2 reserve list for use by the Universal Postal Union. The decision was later reversed, with Ascension Island now the sole outlier. (Three other ccTLDs, gg (Guernsey), im (Isle of Man) and je (Jersey) also fell under this category from 1996 until they received corresponding ISO 3166 codes in March 2006.)
eu (European Union): On September 25, 2000, ICANN decided to allow the use of any two-letter code in the ISO 3166-1 reserve list that is reserved for all purposes. Only EU currently meets this criterion. Following a decision by the EU's Council of Telecommunications Ministers in March 2002, progress was slow, but a registry (named EURid) was chosen by the European Commission, and criteria for allocation set: ICANN approved eu as a ccTLD, and it opened for registration on 7 December 2005 for the holders of prior rights. Since 7 April 2006, registration is open to all.
tp (the previous ISO 3166-1 code for East Timor): To be phased out in favour of tl during 2005.
yu (the previous ISO 3166-1 code for Serbia and Montenegro, when it was still known as Yugoslavia)

Unconventional ccTLD usage

Lenient registration restrictions on certain ccTLDs has resulted in domain names like I.am, start.at and go.to. Other variations of ccTLD usage have been called domain hacks, where the Second-level domain and ccTLD are used together to form one word or one title. This has resulted in domains like blo.gs of South Georgia and the South Sandwich Islands (gs), del.icio.us of United States of America (us), and cr.yp.to of Tonga (to). (Non country code TLDs have also been used, like inter.net which uses the .net gTLD, probably the first domain hack ever.)

Historical ccTLDs

There are two ccTLDs which have been deleted after the corresponding 2-letter code was withdrawn from ISO_3166-1, namely cs (for Czechoslovakia) and zr (for Zaire). There may be a significant delay between withdrawal from ISO 3166-1 and deletion from the DNS; for example, ZR ceased to be an ISO 3166-1 code in 1997, but the zr ccTLD was not deleted until 2001. Other ccTLDs corresponding to obsolete ISO 3166-1 have not yet been deleted; in some cases they may never be deleted due to the amount of disruption this would cause for a heavily used ccTLD. In particular, the Soviet Union's ccTLD su remains in use more than a decade after SU was removed from ISO 3166-1.