The gateway service using the Z39.50 protocol in a web form has been discontinued. Searches from this page to other library catalogs around the world using Z39.50 are no longer maintained here. The Z39.50 search service is still available as embedded in Library platform software.
Configuration specifications for Z39.50/SRU queries are available at: www.loc.gov/z3950/lcserver.html.
Z39.50 Gateway searches of the LC Catalog are now redirected to the responsive web interface at search.catalog.loc.gov:
Z39.50 Gateway searches of the Handbook of Latin American Studies are also now redirected to hlasopac.loc.gov for Keyword Search, Advanced Search, and Browse.
Z39.50 Gateway searches of the National Library Service for the Blind and Print Disabled are also now redirected to NLS Catalog.
Z39.50 is a national and international (ISO 23950) standard defining a protocol for computer-to-computer information retrieval allowing a user in one system (with a Z39.50 client) to search and retrieve information from an other system (with a Z39.50 server) without knowing the search syntax of that system. Z39.50 was originally approved by the National Information Standards Organization (NISO) in 1988.
The Z39.50 Maintenance Agency Page, includes documentation and information related to the development and ongoing maintenance of the Z39.50 standard.
Using a Z39.50 client, it is currently possible to search the Library of Congress bibliographic file. Information that will be required to configure your Z39.50 client to search the LC server directly is provided in LC Z39.50 Server Configuration Guidelines.
last edit February 18, 2026