In order to make materials accessible in some sort of locating tool like an online catalog, and to facilitate browsing of the library shelves, libraries attempt to organize and shelve materials about the same subject matter together. Resources are often about more than one idea or subject. Most cover a number of different subjects and some cover two or three subjects in equal depth. Deciding which subject into which the resource will be classified will have implications for the person seeking the resource.
The two major classification systems used in American libraries to organize library materials are the Dewey Decimal Classification System and the Library of Congress Classification System. Both systems organize resources into subject categories and allow libraries to shelve similar items together. Dewey is the older of the two systems and is used mostly by public libraries and small academic libraries. The Library of Congress Classification System is used predominately by academic libraries and other libraries that have large research collections.
Library of Congress Classification System
The Library of Congress Classification System was developed by the Library of Congress in Washington, DC in the early 1900's to organize the collections of the Library. The Library of Congress chose to develop its own classification system rather than use the Dewey Decimal Classification System because of the large size of its collection--the Dewey system was not considered flexible enough to meet the needs of the LC collection. SHC and most U.S. research and academic libraries have adopted the Library of Congress Classification System.
The Library of Congress Classification System organizes knowledge into twenty-one broad categories. The first letter of a Library of Congress call number indicates the general subject area. The second letter indicates the specific subject section within the general category.
Look at the Library of Congress Classification System and notice the subdivisions within broader areas of knowledge.