Before the advent of the online catalog in 1980, the card catalog served as the primary way to find books and periodicals in the Library's vast collections. The online catalog provides an array of options for locating materials held by the Library, including options to search by keyword, author, title, subject, format, Library location, and other designations. While the card catalog does not provide the same flexibility in searching, it does provide access through subject, author, and title cards.

Subject cards allow for identification of works based on their subject; author cards allow for identification of works by an individual or corporate author; and title cards allow for identification of works by title. These cards are interfiled and arranged alphabetically. The alphabetical arrangement has some exceptions. Most notably, personal names are filed first; place names are filed second; subjects are filed third; and titles are filed last. Here is a sample arrangement:

• Orange, James [personal name]
• Orange, Connecticut [place name]
• ORANGE—MARKETING [subject heading]
• The orange cat [title]

When looking for a specific book, you can check the catalog under the book's title. The title will be typed in small letters at the top of the card, as in the following example:

You could also search under the author's name (last name, first name), and check the cards files under the name for a book record. Here is an example of an author card for Charlotte Brontë for an edition of Jane Eyre:

The final way to search is by subject. Since 1898, the Library has assigned Library of Congress Subject Headings (LCSH) to cataloged items in its collections. LCSH can be described as tags or standardized terms that describe what a particular book is about. They allow researchers to effectively search for materials by subject, rather than by title and author.

As the world around us changes, so too do the terms we use to describe events within it, and it is important to know the correct LCSH for a subject in order to locate subject cards for it in the card catalog. For instance, researchers checking the card catalog for books about World War I need to know that the LCSH under which relevant works can be found is not World War, 1914-1918, the current LCSH for subject, but rather European War, 1914—. Similarly, researchers exploring books about cooking and cookbooks need to know that the LCSH for these subjects used in the card catalog is Cookery, as seen in the following example:

The subject headings used by the Library of Congress when the card catalog was discontinued in 1980 can be identified through the 9th edition (1980) of Library of Congress Subject Headings. These are large red volumes, and can be found on a table in Deck 33 and on a shelf when you enter Deck 37. If you are not certain of the correct subject heading used for a particular topic, you can consult these volumes to identify the correct heading. Feel free to ask a reference librarian for assistance.

When searching by subject, please note that subject cards are stained red on the top edge, and the subject headings, as in the example above, will be typed in capital letters at the top of the catalog card.

A sign at a table in Deck 33, reproduced below, provides additional tips on searching the card catalog. Please note that the Library no longer uses paper call slips to submit book requests, so details about call slip requesting on it should be ignored.