UKAT is a subject thesaurus which has been created to support indexing and searching in the UK archive sector. UKAT should promote greater consistency in the subject indexes created by individual archive repositories, and by the projects which make up the strands of the emerging national archives network. Any gateway (or gateways) created for the network, such as that proposed by the Linking Arms project, will need a common terminology to ensure that users' subject searches retrieve all relevant records, across all the sets of data linked to the gateway. A shared standard for subject indexing will help the national archives network to achieve its subject searching potential, benefitting both archive services and their users.The backbone of UKAT is the UNESCO Thesaurus (UNESCO), a high-level thesaurus with terminology covering education, science, culture, the social and human sciences, information and communication, politics, law and economics. UNESCO was used as the basis for UKAT because of its adoption for indexing purposes by a number of archives and archive projects, including the National Archives, Archives in London and M25 Area (AIM25), Access to Archives (A2A), CASBAH (Caribbean, Black and Asian Studies), Gateway to Archives of Scottish Higher Education (GASHE), MUNDUS (missionary archives), and the Archives Hub (which also uses Library of Congress Subject Headings). However, while UNESCO covers a broad range of subject areas, it often lacks the depth of detailed terminology required by archives for indexing. It was therefore decided that UKAT should extend and adapt UNESCO to incorporate indexing terms which repositories and projects had devised themselves or incorporated from other schemes, such as Library of Congress Subject Headings or the British Education Thesaurus. UKAT has thus been created as a thesaurus conforming to international standards, with the coherent structure of UNESCO, but also significantly enhanced to include terms of relevance to the archive community and its users. Particular emphasis has been given to incorporating terms reflecting the histories and experiences of groups which are under-represented among archive users, to encourage their participation in the archival heritage in line with national priorities for the sector.