Each volume of LC has an index, and all categories can be used as independent professional classification tables. LC*** is divided into 20 categories: comprehensive works; Philosophy and religion; C history: auxiliary science; D history: world history; E-F history: American history; Geography and anthropology; Social science; Political science; K method; L education; M music; N art; P language and literature; Q science; R medicine; Agriculture and animal husbandry; Testing technology; U military science; V. Naval science; Bibliography and library science. The classification number consists of letters and numbers, and the number part is numbered in integer order. This classification is practical and meticulous, which is not only applicable to comprehensive libraries, but also to professional libraries. The classification number of LC is recorded in the cataloging data of Britain and the United States, printed cards issued by the Library of Congress of the United States and machine-readable catalogues of several countries.