LCLibrary of Congress Subject Headings is the largest general-purpose subject heading system in the world, and one of the longest-running controlled vocabularies in continuous use. Maintained by the Library of Congress since 1898, LCSH provides the subject access infrastructure for millions of bibliographic records in libraries across the United States and internationally.
Background
LCSH traces its origins to 1898, when the Library of Congress began developing a standardized list of subject headings to organize its rapidly growing collections. The first printed edition appeared in 1914 as Subject Headings Used in the Dictionary Catalogs of the Library of Congress. Over the following century, the vocabulary expanded through cooperative cataloging efforts, where participating libraries contributed headings through the Subject Authority Cooperative Program (SACO). The transition to machine-readable formats began with MARC authority records and has continued with the publication of LCSH as linked data through the LC Linked Data Service, launched in 2009.
Purpose & Scope
LCSH serves as the primary subject access system for library catalogs, enabling users to find materials on a given topic regardless of the specific words used in a title or description. The vocabulary encompasses:
- Topical headings -- concepts, events, objects, and activities
- Geographic subdivisions -- place-based refinements
- Chronological subdivisions -- time-period qualifiers
- Form/genre subdivisions -- describing what a work is rather than what it is about
- Free-floating subdivisions -- standard modifiers applicable across headings
- Children's (AC) headings -- simplified headings for juvenile materials
LCSH also includes validation strings -- pre-coordinated heading combinations programmatically verified against bibliographic records.
The scheme is organized as a SKOS Concept Scheme and a MADS/RDF Scheme, with broader, narrower, and related term relationships forming a rich syndetic structure.
Collections
The LC Linked Data Service organizes LCSH into several sub-collections:
| Collection | Description |
|---|---|
| Authorized Headings | The main set of established subject headings |
| General Collection | The broadest set of headings |
| Children's Headings | Headings designated for juvenile materials |
| Subdivisions | Topical, form/genre, temporal, geographic, and language subdivisions |
Serializations & Technical Formats
LCSH is available in a wide range of serializations through the LC Linked Data Service at http://id.loc.gov/authorities/subjects. Individual records can be retrieved in MADS/RDF and SKOS formats, each available as RDF/XML, N-Triples, and JSON. Bulk downloads are provided in compressed archives covering MADS/RDF and SKOS/RDF in JSON-LD, N-Triples, Turtle, and XML formats.
The base URI for the scheme is http://id.loc.gov/authorities/subjects, and individual headings follow the pattern http://id.loc.gov/authorities/subjects/sh{identifier}.
Governance & Maintenance
LCSH is maintained by the Policy, Training, and Cooperative Programs Division of the Library of Congress. New headings and changes are proposed through SACO, which coordinates contributions from libraries participating in the Program for Cooperative Cataloging (PCC). The vocabulary is continuously updated; the last record update as of indexing was March 10, 2026.
As a work of the United States government, LCSH data is in the public domain.
Notable Implementations
LCSH is used by virtually every academic and research library in the United States, and by many national libraries and library networks worldwide. It forms the basis of several derivative vocabularies, most notably FAST (Faceted Application of Subject Terminology). The Repertoire de vedettes-matiere (RVM) is a French-language adaptation used in Canadian libraries. Many national bibliographies reference LCSH or use it as a mapping target for interoperability with local subject systems.
Related Standards
- FAST -- a simplified, faceted adaptation of LCSH developed by OCLC Research
- MADS/RDF -- the Metadata Authority Description Schema used to encode LCSH as linked data
- SKOS -- the Simple Knowledge Organization System vocabulary used as an alternate encoding