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The Library of Congress Card Catalog

Frequently Asked Questions

What is the origin of the card catalog's classification system?

When the Library of Congress was founded in 1800, its original collection consisted of 728 books and three maps. By 1897, when the Library relocated from the U.S. Capitol to the Thomas Jefferson Building (then known as the Congressional Library, or the Library of Congress Building), the Library's collection has grown to more than 787,000 books and 218,000 pamphlets (Annual Report of the Librarian of Congress, 1897, p. 4 External).

During its time in the U.S. Capitol, the Library issued nine major catalogs documenting its collections, as well as dozens of catalog supplements. On August 24, 1814, the Library's collections were destroyed when the British burned the Capitol. Early in 1815 Congress agreed to purchase Thomas Jefferson's personal library of 6,487 volumes to reconstitute the Library collections. When the Library published a new catalog of its collections in 1815, the catalog adapted the classification scheme used by Thomas Jefferson for his personal library.

Jefferson's classification system derived from Sir Francis Bacon, who believed that all learning stems from one of three faculties: Memory, Reason, and Imagination. These categories were renamed by Jefferson to describe three fields of knowledge: History (Memory), Philosophy (Reason), and Fine Arts (Imagination). Jefferson broke down these three categories into multiple subclasses, eventually denoting a "Chapter" to each subclass. Jefferson's 44 Chapters, with some modifications, formed the basis of the Library's classification system from 1815 through the end of the 19th century. An image of showing the list of Chapters follows below.

Thomas Jefferson's classification system as it appears in Catalogue of the Library of the United States... [1815].

What do the fractions on some older catalog cards mean?

The Library of Congress issued its final classified print catalog in 1861. After this, the Library began a reclassification project that resulted in the creation of more than ten-thousand topical and geographical divisions and subdivisions by 1897. During this reclassification period, the Library’s bookshelves in the Capitol were numbered, and "call numbers" generated based on a modified form of Jefferson's numerical classification system combined with the numbers assigned to the Library shelves in the Capitol. The resulting numbers, which look like fractions, appear on some catalog cards for nineteenth and early twentieth century books.

Card catalog record with a "Jeffersonian fraction" call number.

The “numerator” of the fraction designates which of the forty-four “Chapters," External or “main classes,” to which an item belongs; while the “denominator” is the number of the shelf on which the book could be found. As a hypothetical example, the number 35/2718 would be a book of “Fiction” (Chapter/Class 35) found on shelf 2718. In the real example provided above, for a published report by Ferdinand Peck, the numerator "15" is for Chapter 15 of Jefferson's classification system, covering the "Useful Arts." The denominator "9185" refers to the physical shelf location of the book when it was housed in the Capitol.

There is no practical way to translate these main Chapters and their subdivisions into modern LC classification numbers.

I've heard that there is a secret copy of card catalog in the basement of the Library. Is this true?

The card catalog in the Library's Main Reading Room was created for use by the public. However, another version of this "Main Catalog" existed exclusively for use by Library staff. This other version of the card catalog, known as the "Official Catalog," was used by Library staff to aid in acquisitions (for instance, determining which books were not held by the Library) and in cataloging new additions to the Library. It was begun slightly after the Main Catalog, and can easily be distinguished from the Main Catalog because it has no rods in the trays so that staff could easily remove and add cards.

Part of the "Official Catalog" located in the sub-basement of the Library's James Madison Building. October 2023. Photo by Peter Armenti.

The Official Catalog was originally located on the Second Floor of the "Annex," or Adams Building (view a map from the 1950 Cataloging Maintenance Division manual showing the catalog's location External). The Official Catalog eventually was relocated to Room 542 of the Madison Building, and then in December 1985, as noted in the December 9, 1985, issue of the Library of Congress Information Bulletin (see the "Renovation Moves" notice External), to the sub-basement.

On top of the Official Catalog rest hundreds of red buckram portfolios from the Library’s former sheet shelflist External, which served as a record of the books held by the Library in the order that they appeared on the shelves (classification order). As noted in Subject Cataloging Manual: Shelflisting (1995):

The Library of Congress sheet shelflist, created between 1897 and 1940, was the forerunner of the card shelflist. The sheet shelflist was originally maintained on sheets encased in red buckram portfolios, although some classes (M, Z, and parts of P) were recorded on 3x5” cards. Holdings and location information were listed, including holdings for serials. In 1940 all newly processed entries began to be listed on cards and interfiled into the existing card shelflist.

Portfolios from the Library of Congress's old shelflist rest on the top of the Official Catalog in James Madison Building. October 2023. Photo by Peter Armenti.

An image of the first page of the first portfolio of the sheet shelflist shows the arrangement of several titles in the AC subclass:

The first page of Portfolio 1 from the sheet shelflist. October 2023. Photo by Peter Armenti.

The holdings information listed in the sheet shelflist was not fully integrated into the card shelfist. Instead, during the late 1990s a contractor converted holdings information from the sheet shelflist (2,200 portfolios of approximately 1,000,000 entries), as well as holdings and location information for the twelve-million cards in the card shelflist and 900,000-title serials check-in file, for inclusion in the Library's online Voyager system. The card shelflist was subsequently closed in 1999, and in 2004-2005 dispersed among numerous cataloging teams housed in the Jefferson and Adams buildings. A timeline of significant events in the Library's shelflisting history is available through the online edition (2013) of the Classification and Shelflisting Manual (PDF, 133 KB).

Did different Library divisions keep their own card catalogs?

Yes, many Library reading rooms and divisions maintained separate card catalogs documenting the holdings of all or part of their collections. A summary of various card catalogs maintained by Library reading rooms and divisions at the end of 1954 appears in The Card Catalogs of the Library of Congress: A Brief Description (1955), which is available online through HathiTrust Digital Library External. The second edition of this work, published in 1983, also is available through the HathiTrust External and documents Library card catalogs available through 1982.

Several reading rooms and divisions, such as our Moving Image Research Center, continue to maintain card catalogs that document a portion of their older, special collections. The Newspaper and Current Periodical Reading Room also maintains an up-to-date card catalog of foreign and domestic newspaper microfilm currently received. Some of the records included in them remain unavailable through the Library's online catalog. If you want to know whether a particular reading room still maintains a card catalog that may need to be searched for materials held by the Library, contact that reading room directly.