AIM25 (Archives in London and the M25 area), a project funded by the Research Support Libraries Programme (RSLP) , and led by King's College London, provides a single point of networked access to collection descriptions of archives held in 49 higher education (HE) institutions and learned societies in the greater London area. The project has intended, where possible, to be comprehensive in its coverage of holdings by including deposited collections, in a wide range of subject areas, and also the administrative records of the participating institutions. The latter have been a neglected historical resource, but are of value for a range of research topics, for instance biography, social mobility, and the history of individual academic disciplines. AIM25 is thus encouraging greater awareness of all these archival collections, some of which have never been described before. The project commenced in January 2000 and will run until July 2002. Further details on the project, its partners and their archives are available on the AIM25 website. 
A central team, consisting of five peripatetic archivists, compiles descriptions in the HE partner institutions. Participating institutions can also submit descriptions themselves. The Project Coordinator also provides editorial support for descriptions submitted by 'external' (non-HE) partners. The approach of using this regional cataloguing team has proved extremely beneficial: the team members' familiarity with data entry and cataloguing standards has produced consistent and high-quality descriptions. Moreover this project methodology has permitted institutions with limited cataloguing facility to participate because it does not divert host staff from their other duties.
Smaller archive collections are covered by a single description. Several descriptions are produced for larger collections (particularly institutional records), each covering a discrete sub-collection or series. Descriptions conform to the ISAD(G) (General International Standard Archival Description) format.  AIM25 data is held centrally at the University of London Computer Centre in a MySQL relational database , which interacts with a web interface via PERL scripts. Collection description records can be input and edited via online templates or imported singly or in batch from a number of standard formats. Records have been imported from proprietary cataloguing systems such as ADLIB, CAIRS, CALM and HDMS. The database is also capable of exporting descriptions to these and other database systems in any specified format which can be mapped to ISAD(G).
The AIM25 website allows researchers to browse descriptions by repository, to conduct searches using keywords/text or to search using indexes of personal, corporate and place names and a subject thesaurus. Personal and corporate names are formulated according to the National Council on Archives Rules for the Construction of Personal, Place and Corporate Names (1997).  Like other UK archival bodies such as the Public Record Office  and UK National Digital Archive of Datasets , AIM25 chose the UNESCO Thesaurus  as the basis for its thesaurus. Indexing terms are linked to descriptions using the online editing functions, and each night new web pages are generated which list the terms currently linked to descriptions and the sources of the terms. The selection of a term by the user retrieves a copy of the description. Terms are listed alphabetically for personal, corporate and place names and for subjects, and - following the UNESCO Thesaurus - hierarchically for places and subjects. Because of the wide range of subject specialisations of the participating repositories, the thesaurus also includes terms added from other sources, including specialised thesauri such as the British Education Thesaurus, the Australian Human Services and Health (HSH) thesaurus (which is a more concise version of the National Library of Medicine list of medical subject headings -MeSH), and Library of Congress Subject Headings (LCSH). The thesaurus also includes specialised groups of terms which have been developed by projects or services explicitly within the UNESCO framework to provide finer-grained indexing (the Public Record Office, SOAS Missionary thesaurus, and AIM25 itself). The source of each indexing term is also recorded in the database, and used to indicate a term's thesaural origin in the thesaurus search pages.
An electronic version of the UNESCO Thesaurus is mounted in MySQL tables corresponding to the relationships within UNESCO (broader/narrower terms, related terms, and preferred terms), and these term-relationship associations are used to build the thesaurus hierarchy search pages. Where non-UNESCO terms have been used, and those terms were developed as UNESCO extensions, the software generating the hierarchy search pages does not distinguish terms from different sources but produces a seamless listing of the combined set of indexing terms. In the case of HSH and LCSH, the same applies if terms in those thesauri match exactly terms in the extended UNESCO hierarchy; where this occurs, the UNESCO-based hierarchy inherits any HSH/LCSH terms related to the matching term. Where HSH or LCSH terms are required for indexing AIM25 descriptions but do not passively match terms in the extended UNESCO hierarchy, these are linked manually into the hierarchy by project archivists.
AIM25 forms a strand in the developing UK National Archive Network (NAN)  envisaged by the National Council on Archives (NCA) in its reports Archives On-Line: the establishment of a UK archival network (1998)  and British Archives: The Way Forward (1999) . AIM25 data is structured in such a way that it is platform independent and can be exported to other systems in a variety of formats and through a range of protocols to permit easy exchange of information and cross searching. Interoperability is achieved in several different ways:
The AIM25 website currently hosts over 3,200 descriptions, with another 1,000 to be added during the course of March and April 2002. In December 2001, AIM25, along with three other strands of the NAN (A2A, the Archives Hub, and SCAN) participated in a series of six joint user-evaluation exercises of their interfaces, funded by Resource (the Council for Museums, Archives and Libraries) . The findings are expected to be published on the Resource website in March 2002. Following the evaluations, refinements have already been made to the AIM25 web interface which should increase ease of use. Evaluation of the technical architecture will also be made before the project terminates in July 2002. Usage of the website has increased from registering some 20,000 hits in February 2001 to nearly 80,000 hits (from some 42 countries) in January 2002.