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Library of Congress Subject Headings (LCSH) is a controlled vocabulary of standardized subject terms used to describe what library materials are about. Researchers use it to move from a loose keyword to the exact heading libraries use, then to browse broader, narrower and related headings. This page maps the Library of Congress files that make up the LCSH ecosystem and explains which one answers which question.
What are Library of Congress subject headings?
LCSH is a subject indexing language. Instead of every cataloguer inventing a phrase for a topic, the Library of Congress maintains one authorized heading per concept, so every item on that topic is described with the same words. The Library of Congress describes LCSH as perhaps the most widely adopted subject indexing language in the world and says it has been actively maintained since 1898 (loc.gov/aba/cataloging/subject, read 2026-11-07).
Who runs it and what it covers
The Library of Congress maintains LCSH. Proposals for new and revised headings are reviewed regularly at staff meetings of its Policy, Training, and Cooperative Programs Division, and approved changes are published as lists. Libraries outside the Library of Congress can propose headings through the Subject Authority Cooperative Program (SACO). The process is documented on the Library of Congress page “Process for Adding and Revising Library of Congress Subject Headings”.
Which Library of Congress file answers which question
| Need | File or tool | What the Library of Congress says it is |
|---|---|---|
| The list of headings | LCSH, 47th edition (free PDFs) | Print-ready PDFs: an introduction, Numerals, and each letter A to Z. Data for the 47th edition was selected in April 2026. |
| Which subdivisions can follow a heading | Free-floating subdivisions (PDF) | Published separately, with its own introduction. |
| The rules for building and assigning headings | Subject Headings Manual (SHM) | Numbered instruction sheets H 0000 to H 2400, plus a glossary, Appendices A to G and an index. |
| Genre or form of a work | Library of Congress Genre/Form Terms (LCGFT) | A separate vocabulary, published separately from LCSH. |
| Where an item sits on the shelf | Library of Congress Classification | A different system; see Library of Congress classification numbers. |
How to find and use Library of Congress subject headings
The Library of Congress publishes LCSH as free PDFs, and states it will continue as part of the web-based subscription product Classification Web Plus. The authorities.loc.gov search tool and the id.loc.gov Linked Data Service are the Library of Congress online routes to authority records. The practice below is a research strategy, not interface instructions for those tools.
How to use Library of Congress subject headings for literature discovery
- Start with your own keyword, then look it up in LCSH to find the authorized heading for the concept.
- Read the authority record or PDF entry for the references it gives to broader, narrower and related headings, and note any “use” references that redirect a variant term to the authorized one.
- Search a library catalogue using the authorized heading, then repeat with the narrower and related headings to widen or focus the set.
- Keep the heading’s subdivision pattern, written Topic–Subdivision, as part of the search where the catalogue indexes it.
- Pair this with keyword searching: headings describe an item as a whole and cannot capture a term an author coined last month. For search technique across databases see Boolean search operators for literature searching.
Which edition to use
The Library of Congress states that earlier editions are archived and should not be used for cataloguing. Use the current edition (the 47th as of 2026-11-07). The Subject Headings Manual page notes that, as a result of the decision to cease using form subdivisions, the manual is being significantly updated, so check the date on any instruction sheet you rely on.
Subdivisions and the Subject Headings Manual
A heading can be refined with subdivisions. In the Subject Headings Manual, H 1075 covers subdivisions, H 1090 multiple subdivisions and H 1095 free-floating subdivisions (all revised February 2026). The H 1100 to H 1146 sheets cover free-floating subdivisions by type, including H 1100 Classes of Persons, H 1110 Names of Persons, H 1140 Names of Places and H 1146 Pattern Headings. H 0180, Assigning and Constructing Subject Headings, was also revised in February 2026. Sheets H 0600 to H 0900 cover chronological and geographic headings.
Strengths and limits
- Strength: one authorized heading per concept gives consistent retrieval across items described by different people.
- Strength: broader, narrower and related references let a researcher move through a topic systematically.
- Limit: headings are assigned by cataloguers, so an item is only as findable as its catalogue record; headings are not a substitute for keyword searching of full text.
- Limit: the vocabulary changes through the proposal process, so older records may carry superseded forms, and the subdivision rules are in revision.
Alternatives and related vocabularies
| Vocabulary | Maintained by | Relationship to LCSH |
|---|---|---|
| LCGFT | Library of Congress | Describes genre and form, published separately from LCSH. |
| MeSH | US National Library of Medicine | Controlled vocabulary used for PubMed indexing; see MeSH terms in PubMed. |
| GND | German-language library community | Authority file that includes subject headings; see GND authority file. |
For choosing your own author keywords alongside controlled terms, see how to choose keywords for a research paper.
FAQ
What are Library of Congress subject headings?
They are the Library of Congress controlled vocabulary of authorized subject terms, maintained since 1898 and used to give each topic one consistent heading.
How can I find Library of Congress subject headings?
Download the free LCSH PDFs (47th edition) from the Library of Congress, or use its authorities.loc.gov and id.loc.gov services. Many library catalogues also display the headings on each record.
What is the Library of Congress subject headings list?
It is the LCSH edition published as PDFs: an introduction, Numerals, and letters A to Z, with a separate PDF of free-floating subdivisions.
How to use Library of Congress subject headings?
Look up your keyword to find the authorized heading, follow its broader, narrower and related references, and search a catalogue with those headings alongside keywords.
Sources
- Library of Congress, Subject Headings and Genre/Form Terms, read 2026-11-07.
- Library of Congress, Library of Congress Subject Headings PDF Files, read 2026-11-07.
- Library of Congress, Subject Headings Manual, read 2026-11-07.
