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 developed by Thomas Jefferson. By the time of Putnam's departure from his post 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, 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 libraries use NLM in conjunction with LCC, eschewing LCC's R (Medicine).
|A||Class A -- General Works|
|B||Class B -- Philosophy, Psychology, Religion|
|C||Class C -- Auxiliary Sciences of History|
|D||Class D -- History, General and Old World|
|E||Class E -- History of America|
|F||Class F -- Local History of the United States and British, Dutch, French, and Latin America|
|G||Class G -- Geography. Anthropology. Recreation|
|H||Class H -- Social sciences|
|J||Class J -- Political science|
|K||Class K -- Law|
|L||Class L -- Education|
|M||Class M -- Music|
|N||Class N -- Fine Arts|
|P||Class P -- Language and Literature|
|Q||Class Q -- Science|
|R||Class R -- Medicine|
|S||Class S -- Agriculture|
|T||Class T -- Technology|
|U||Class U -- Military Science|
|V||Class V -- Naval Science|
|Z||Class Z -- Bibliography. Library Science. Information resources|