Library of Congress Subject Headings (LCSH) should be considered a grand index to the Library of Congress Classification System. Every book in the library has unique subject headings assigned to it (e.g., Animal Rights). Think of these subject headings as tags that help you find all the material the library has on a particular topic. All the books on a topic can be identified and located by looking up the correct subject terms in the library's catalog. And, by using this uniform approach, all books about a particular topic will be shelved near each other in the stacks.
The updating of subject headings is a continuous process and each year more than 5,000 headings are added. Currently there are more than 200,000 subject headings!
Large subject topics are divided with specific subdivisions. A large topic like AIDS is divided by using many subdivisions that allow you to zero in on government policy, for instance if that is your focus. Topics that are related to the one you searched for are listed as related terms (RT). Small topics will even have the broader divisions listed. By using the broader terms (BT) you can find more general information. Using the narrower terms (NT) can narrow topics that seem a little too big.
Example of an LC Subject Heading:
