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Library Basics: Library of Congress Subject Headings

Learn the basics of searching the library, what the Library of Congress Classifications are and where to find them in our library

Library of Congress

Library of Congress Subject Headings

Introduction to LOC Subject Headings

Introduction to LOC Subject Headings

Controlled Vocabulary

Subject headings provide one of the primary search techniques you may use in retrieving information from resources in the ISU Library. They may be used in both print and electronic sources. The strength of subject headings (often called descriptors) is that they allow us to use a controlled vocabulary to organize information in a logical fashion. The goal is to make it easier for you to find the specific information you need.

A "controlled vocabulary" is a set of standard terms used to describe the contents of items found in a database. This includes the contents of books in the library and articles listed in an index. A term in a "controlled vocabulary" may describe a person, an event, an idea, or a place.

In libraries, we usually refer to the controlled vocabulary as subject headings. The ISU Library, in common with most academic libraries, uses the Library of Congress Subject Headings. This is a huge list of descriptive words and phrases which is published in four large, red volumes. Most of the records for books you will find in LUIS (the Libraries online catalog) have one or more subject headings attached to them. Periodical indexes often refer to their controlled vocabulary terms as descriptors, but they all mean the same thing.

controlled vocabulary is an important way of drawing together, under a single word or phrase, all the material that is available on a particular topic. The purpose is to take the "guesswork" out of searching. We tend to have many different ways of describing the same concept. For example, let's say you're trying to find all the information you can in the library on the topic of the Civil War. What term would you use to search? Civil War? There have been a lot of those in many different countries. American Civil War? U.S. Civil War? United States Civil War? Civil War in the United States? War Between the States? War of Secession? War of the Rebellion? The Lost Cause? The choices are almost endless.

Does that mean you have to think up all these different synonymous terms in order to find everything you can on the topic? Not if you use a controlled vocabulary. For example, if you look up the term American Civil War in the Library of Congress Subject Headings you find that the subject heading to use is United States -- History -- Civil War, 1861-1865. That may seem a rather awkward or ponderous term to search, but using it will bring you a list of all the books the University Libraries have on the Civil War in a single search!

It's important to remember to check the subject heading books before searching. A subject search in LUIS on "Vietnam War", for instance, turns up only 47 entries, far fewer than one would expect on so important a topic. You must use the subject heading Vietnamese Conflict, 1961-1975 to find material on that subject.  This search reveals 996 entries, which is more like it!

Periodical indexes, both print and electronic, also allow you to search for articles using a controlled vocabulary. For example, if you looked for articles on "freedom of religion" in a recent annual volume of the Social Sciences Index (a print index), you would be referred to the subject heading Religious liberty. Under that term, you would find a list of all the articles on freedom of religion published during that year by the journals that the Social Sciences Index covers.

By drawing together all items on the same topic under a single word or phrase, a controlled vocabulary can make searching for information much easier.

How to use Subject Headings


This is only a very brief introduction to the essentials of subject headings. If you need to conduct more sophisticated searches or have any problems or questions, please ask one of the Reference Librarians for assistance.  You may also use the form for Online Questions and Comments or chat online with a Reference Librarian at Reference Live.

Revised October 2, 2001

ACKNOWLEDGEMENTS: This page is adapted from the McFarlin Library Web site at The University of Tulsa, and is kindly used with their permission.