All ASCII ccTLD identifiers are two letters long, and all two-letter top-level domains are ccTLDs. In 2010, the Internet Assigned Numbers Authority (IANA) began implementing internationalized country code TLDs, consisting of language-native characters when displayed in an end-user application. Creation and delegation of ccTLDs is described in RFC 1591, corresponding to ISO 3166-1 alpha-2 country codes.
IANA is responsible for determining an appropriate trustee for each ccTLD. Administration and control is then delegated to that trustee, which is responsible for the policies and operation of the domain. The current delegation can be determined from IANA's list of ccTLDs. Individual ccTLDs may have varying requirements and fees for registering subdomains. There may be a local presence requirement (for instance, citizenship or other connection to the ccTLD), as for example the Canadian (ca) and German (de) domains, or registration may be open.
Almost all 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 dependency Bouvet Island (bv) and the designation 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. Two French territories, bl (Saint Barthélemy) and mf (Saint Martin), await local assignment by France's government.
The code eh, although eligible as ccTLD for Western Sahara, has never been assigned and does not exist in DNS. Only one subdomain is still registered in gb (ISO 3166-1 for the United Kingdom) and no new registrations are being accepted for it. Sites in the United Kingdom generally use uk (see below).
The former .um ccTLD for the U.S. Minor Outlying Islands was removed in April 2008. Under RFC 1591 rules .um is eligible as a ccTLD on request by the relevant governmental agency and local Internet user community.