The Subject search in the ELAC Library catalog uses the Library of Congress Subject Headings (LCSH). These are terms selected by librarians to help people find what they need in a library catalog or an article database. Librarians assign LCSH subject headings to each item in the catalog to make it easy to find other material on the same or similar topics.

LCSH subject headings work hierarchically, in levels from general to specific. For example, if you wanted to find books on California history, the LCSH subject heading would start with the broad category "California" and narrow that down using the term "history." After that, subheadings such as time periods and topics break the organization down even further. It may help to envision it like this:

Library of Congress Subject Headings also help deal with the problem of having more than one term describe the same or similar topics. For example, what if a library had some books shelved under "Farming" and others under "Agriculture?" Depending on the search term you used, you'd only find some of what the library had to offer on the subject! So, the LCSH use one term – in this case "agriculture" – to group the relevant material under a single heading. This can be a problem if you don't already know the word that LCSH uses for a subject -- so if you enter a term not used by LCSH, often you will find a reference directing you to the appropriate term.