As in other parts of the Library of Congress, the Library's online catalog can be used to find books and periodicals in the Law Library collections. It is important to gain some familiarity with classification of legal materials, specific subject headings, and catalogs that may be helpful.

The Law Library collections have various classification numbers (or call numbers). Most law materials are in class K, which is often subdivided according to country:

• K is international law
• KF is United States law
• KD is British law
• KZ is used to classify international treaties

A card catalog is also available and is helpful for finding books that were published before 1980 for which the classification number is not given in the online catalog. Books written in non-roman-script languages that do not have transliterated titles can also be located through the card catalog.

The Law Library Reading Room Card Catalog can be used to find call numbers for materials that are not available through the Library's online catalog. Many of the rare materials have not been cataloged and given a Library of Congress call number, and for these, the card catalog may be one of the only sources for finding a particular book or series. Other, published catalogs are also helpful and should be consulted to identify useful material.