Library of Congress

Online Catalog

Library of Congress > LC Online Catalog > About the LC Online Catalog
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Scope of the Catalog

Library of Congress collections contain over 158 million books, periodicals, manuscripts, maps, music, recordings, images, and electronic resources. More than 18 million records describing these collections are located in the LC Online Catalog. You can search these records by keyword or browse by authors/creators, subjects, name/titles, uniform titles, and call numbers. Browse lists also include searching aids such cross-references and scope notes.

Library of Congress cataloging dates back to 1898. The Online Catalog includes many early records (primarily for books and periodicals) created by the Library between 1898 and 1980. These records -- originally maintained in a separate database -- are gradually being updated to reflect contemporary language and usage. Names and subjects found on older records often contain the legend [from old catalog] to indicate possible deviations from current LC practices. In addition, records for some materials cataloged before 1980 are only available to researchers onsite in the Library's Main Card Catalog.

Items in the Library's special collections are generally described as aggregations rather than individually identifying each specific item. LC Online Catalog records for many archival collections are linked to more detailed guides searchable in the Finding Aids system. Records for the Library's still images can be found in the Prints and Photographs Online Catalog; records for portions of Library recordings can be searched in SONIC (Sound Online Inventory and Catalog). Databases, ejournals, and ebooks accessible onsite -- including items found in fee-based online services -- are linked through the E-Resources Online Catalog.

LC Online Catalog Interface

In May 2014, the Library implemented a new user interface to the LC Online Catalog at this address: There were several factors behind this migration decision:

Making the LC Online Catalog Accessible to All

The Catalog's new interface is accessible to all Library patrons including those with disabilities. The Library's experts in assistive technology tested the design with screen readers such as Window-Eyes and JAWS to ensure that patrons who prefer those tools have full access to Catalog functionality. The old user interface did not meet the requirements of the Americans with Disabilities Act (ADA). This interface revision supports the Library’s mission to make its resources available to Congress and the American public.

Flexibility in Design to Enable New Functionality

The new interface allows for greater design flexibility, enabling the Library to more quickly and efficiently expand Catalog functionality. Library developers have already added features such as Cite Record, which provides easy copying and pasting of citations into bibliographies, and the ability to view and save records in MARCXML and MODS. Integration with the Library’s OpenURL resolver FindIt! is planned. The new design also provides better information security for patrons requesting materials from Library collections.

Because the Library's integrated library system vendor no longer maintains the older Catalog interface, enhancements and software fixes will not be made to this product. Development has shifted to the new design, which offers enhanced functionality along with support for the latest versions of popular browsers.

Implementing the Library of Congress Web Standards

By migrating to the new user interface, the Catalog reflects the Library’s latest Web standards and provides the modern look and feel patrons expect with Web search systems. This update brings the Catalog into harmony with the Library’s home page and other LC Web pages, presenting patrons with a more consistent experience across the Library’s Web site.


Reader Registration

Public patrons of Library reading rooms must obtain a Reader Identification Card. These cards are free-of-charge and are valid for two years from the date of issue. Patrons must present in person a valid driver's license, state-issued identification card, or passport at the Reader Registration and Researcher Guidance Office, located in the Madison Building, Room LM 140 (First Floor, near the Independence Avenue entrance <view campus map>).

Patron Account Benefits

Registered readers -- as well as Congressional and Library staff with Library of Congress patron accounts -- may request materials online through the LC Online Catalog using their individual "account numbers." See the Guide for Requesting Materials in the Library's Online Catalog for additional information.

In addition, users with Library of Congress patron accounts have additional privileges in the Library's Primo Central discovery system and the HathiTrust Digital Library:

  • In Primo Central: you can create a personal account that enables you to refine and save search queries as well as save individual citations from your search results. You can also set up alerts for your saved queries that trigger email notifications when new citations are found.
  • In the HathiTrust Digital Library: you can download full PDFs of public domain works that appear in HathiTrust (note that logging on to HathiTrust does not provide access to page images of "Limited (search only)" items). You can also access HathiTrust's Collection Builder, a tool that helps you create and share your personal collections of HathiTrust items for private or public use. Click here for more information on logging in to HathiTrust.

Library Holdings and Availability Information

Records in the LC Online Catalog display holdings and availability information for items -- including their call numbers or shelf location, the Library reading room where they must be requested, and their charge status. Items stored offsite may require additional time to be delivered to the Library campus. Note as well that LC Online Catalog records may indicate the Library holds one copy of a work, even though additional copies may actually be available in the Library's collections.

Please consult reference staff if you have questions about the holdings or availability of Library materials.

Searching Aids

Information from the Library's name and subject authority records is integrated into LC Online Catalog Headings Browse Lists through references (See and See also terms) and scope notes. Search using Browse or click on heading links in individual record displays to see these references.

While it is not possible to store LC Online Catalog search results sets for further manipulation, you may develop more precise search strategies using Advanced Search and the EXPERT option on Keyword Search. These search forms support Boolean operators and nesting; Keyword (EXPERT) also enables you to enter more specific index codes.

Each record in the LC Online Catalog can be referenced with a Permalink, displayed on individual record displays. For records that contain an LCCN, this URL identifier will be an LCCN Permalink; records without an LCCN base their Permalink on the LC Online Catalog system identifier.



This version of the LC Online Catalog complies with the Library of Congress web accessibility guidelines as well as international accessibility and industry standards:

If you have questions or comments on LC Online Catalog accessibility issues, please contact the ILS Program Office at

Special Notes for Libraries and Librarians

Librarians using the LC Online Catalog should note that:

  • Name and subject authority records cannot be directly searched or retrieved in the LC Online Catalog. To search authority records directly, please go to Library of Congress Authorities at
  • It is not possible to store search results sets for further manipulation in the LC Online Catalog, although several thousand records can be saved and exported for manipulation in third-party applications.
  • The Library of Congress uses the international MARC 21 encoding standard to represent and communicate bibliographic, authority, and holdings data in LC Online Catalog records. This standard explicitly characterizes the structure, content designation, and data content (or fields) found in each Catalog record. Some data specific to the Library is contained in locally-defined MARC fields.
  • You can save one or more records from LC Online Catalog search queries in either text or MARC 21 (MARC UTF-8 or MARC-8) formats. Using links in the left panel of individual record displays, records with LCCNs are also available in MARCXML or MODS. In addition, records can be exported using Z39.50/SRU, either through the LC Online Catalog's Z39.50 Gateway or by configuring your Z39.50/SRU client according to the LC's technical guidelines.
  • Number searches by LCCN, ISBN, and ISSN are available from Browse or through number searches using the LC Online Catalog's Z39.50 Gateway.
  • The LC Online Catalog contains records for items in the Library's collections. Therefore, not all records for periodicals in CONSER (Cooperative Serials Cataloging Program) or books cataloged by the Library's Cataloging in Publication program will be found in the Online Catalog.
  • Institutions interested in requesting materials should consult the Library's Interlibrary Loan policy.