Library of Congress Classification is a system for arranging materials in a library. Many large research and university libraries use this system. It provides greater precision in most fields and more room for expansion than the Dewey Decimal Classification (see Dewey Decimal Classification).
Each Library of Congress classification is represented by a set of capital letters and numbers. The first letter in the set indicates one of 21 major areas of knowledge. These areas include: A-general works; B-philosophy, psychology, religion; C to F-history; G-geography, anthropology, recreation; H-social sciences; J-political science; K-law; L-education; M-music and books on music; N-fine arts; P-language and literature; Q-science; R-medicine; S-agriculture; T-technology; U-military science; V-naval science; and Z-bibliography, library science, information resources. The second letter stands for a subclassification. The numbers represent a specific topic.
In the following example, the book Familiar Trees of America, by William C. Grimm, has the number QK 481. The Q stands for science, the K for botany, and the 481 for trees of North America.
The Library of Congress developed its classification system in the early 1900’s for its large collection of books. Specialists frequently add or modify classification numbers to account for current events and new knowledge.
