.gb

.gb is a reserved Internet country code top-level domain (ccTLD) for the United Kingdom, derived from Great Britain.

The domain was introduced with RFC 920^[1] in October 1984 that set out the creation of ccTLD generally using country codes derived from the corresponding two-letter code in the ISO 3166-1 list. However, the .uk domain had been created separately a few months before the compilation of this list.^[2] Consequently, .gb was never widely used. It is no longer possible to register under this domain.

.gb was used for a number of years, mainly by British government organisations and commercial e-mail services using X.400-based e-mail infrastructure. This simplified translating between DNS domains and X.400 addresses, which used "GB" as a country code.^[3]

With the demise of X.400 e-mail and IANA's general aim of one TLD per country, use of .gb declined; the domain remains in existence, but it is not currently open to new domain registrations.

As of 2025, there are at least three subdomains resolving through DNS (although none serve a web page or use): hermes.dra.hmg.gb, delos.dra.hmg.gb, and dfhnet.dra.hmg.gb.^[4] They were originally owned by the Defence Research Agency,^[5] which became the Defence Evaluation and Research Agency in 1995 and was split into QinetiQ and the Defence Science and Technology Laboratory in 2001; the websites became defunct some time thereafter.^[6]

As of November 2022^[update], Central Digital and Data Office's intention was to inform ICANN early in 2023 that the UK wishes to retire the .gb ccTLD.^{[7][needs update]}