In 1815, Thomas Jefferson sold his collection of 6,487 volumes to Congress to replace the 3,000 lost in the flames of 1814, when the British bombarded Washington D. C. When Herbert Putnam became the 2^nd Librarian of Congress in 1899, the collection had grown to the degree that it was glaringly apparent that Jefferson's original classification was woefully inadequate. DDC was considered initially, but Dewey would not permit various changes to his structure requested by Putnam.

Putnam's response was to construct an entirely new scheme, designed specifically for the library's holdings. Putnam based this scheme on Jefferson's original arrangement (based on an interpretation of Francis Bacon's 1605 Advancement of Learning), with contributory elements from Charles A. Cutter. The resultant LC schedules and tables are generally acknowledged to be the best for very large libraries.

LC is an example of a highly enumerative classification based on literary warrant, tailored to the collection on hand. Charles Cutter "built the foundation" for LC in his Expansive Classification (1891-1893), but Putnam elaborated by assigning subject specialists to construct the individucal subject schemes. At present LC is a loosely coordinated series of 21 special classifications, each with its own structure and index, in total comprising more than 10,000 pages. The overarching order is from the general to the specific, from the theoretical to the practical.

Critics of LC emphasize its adherence to conventions long toppled by history, the absence of mnemonic aids, the variance between the degree of coverage in the major classes, and the quarterly revision of the schedules. Nevertheless, LC is used extensively by university, special, and government libraries within and without the United States. Notation is mixed; it consists of one or two letters for main classes followed by four or less ordinal numbers to denote the subdivisions. Further expansion is allowed by gaps between the numbers; when filled, decimals are used. Cutter's author tables and subject numbers facilitate more minute subdivisions alphabetically. Since notation consists of both capital letters and arabic numerals, more combinations and greater specificity is enabled.

Several hundred libraries in the United States have switched from DDC to LC since the 1960's, due primarily to the economic advantages derived from shared cataloguing.