Library of Congress Classification

The Library of Congress Classification (LCC) is a system of library classification developed by the Library of Congress. It is used by most research and academic libraries in the U.S. and several other countries—most public libraries and small academic libraries continue to use the Dewey Decimal Classification (DDC). It is not to be confused with the Library of Congress Subject Headings or Library of Congress Control Number.

The classification was originally developed by Herbert Putnam in 1897, just before he assumed the librarianship of Congress. with advice from Charles Ammi Cutter, It was influenced by Cutter Expansive Classification, and the DDC, and was specially designed for the special purposes of the Library of Congress. The new system replaced a fixed location system originallly developed by Thomas Jefferson.

By the time of Putnam's departure in 1939 all the classes except K (Law) and parts of B (Philosophy and Religion) were well developed. It has been criticized as lacking a sound theoretical basis; many of the classification decisions were driven by the particular practical needs of that library, related to the academic system of the period, rather than considerations of epistemological elegance.

Although it divides subjects into broad categories, it is essentially enumerative in nature. It provides a guide to the books actually in the library, not a classification of the world.

The National Library of Medicine classification system (NLM) uses unused letters W and QS–QZ. Some medically-oriented libraries use NLM for medical subject instead of LCC's R (Medicine), in conjunction with LCC for the rest of the collection.