These resources are at the heart of Special Collections practice, invaluable for helping users and managing collections. Although listed separately to aid understanding, many of these resources increasingly form networks of linked data.

I include several important short-title catalogues (STCs). These abbreviate the very long titles characteristic of early printed books to facilitate the creation of reasonably sized printed publications. This tendency has naturally been relaxed in the online environment although the term STC is still used.

All electronic resources listed are freely available online unless noted. Some offer extra facilities to members or subscribers. The print resources listed are widely held in libraries and most are available in some form online.

If I have missed something important, please do let me know!

Union catalogues

Vast catalogues combining catalogue records from many libraries and archives. These now offer far more than bibliographic look-ups, helping users to discover and access relevant resources.

• 1 WorldCat. ‘The world's largest library catalog’. Managed by OCLC, records for 2 billion items from over 70,000 national, academic and public libraries worldwide. Invaluable for Special Collections in North American universities. www.worldcat.org.

• 2 Jisc Library Hub Discover. 40 million catalogue records from over 165 UK and Irish national, academic and specialist libraries. It replaces, develops and expands two well known union catalogues, COPAC and SUNCAT. https://discover.libraryhub.jisc.ac.uk.

• 3 Karlsrüher Virtueller Katalog (KVK). Via the Karlsrüher Institut für Technologie, 500 million records from libraries in Germany, Austria, Switzerland and worldwide, useful for European early printed books. https://kvk.bibliothek.kit.edu.

Directory of collections

Directory of Rare Book and Special Collections in the United Kingdom and Republic of Ireland (Attar, 2016), a comprehensive guide to collections in all kinds of libraries, alphabetically by location, with indexes by collector and subject.

Archive gateways

Databases connecting finding aids for archival collections.

• 1 Archives Hub. Managed by Jisc, the Hub contains collection-level and multi-level descriptions of collections held in over 350 UK archives. https://archiveshub.jisc.ac.uk.

• 2 Discovery. Discovery is the catalogue of The National Archives (UK). It also hosts descriptions of archives held in other institutions – over 32 million records. http://discovery.nationalarchives.gov.uk.

• 3 Archive Grid. An OCLC project that brings together 4 million archival records, mostly harvested from WorldCat. Useful coverage of US archives. https://researchworks.oclc.org/archivegrid.

• 4 Archives Portal Europe. Records of archives across Europe from over 7,000 organisations, generally managed and input at country level. www.archivesportaleurope.net.