In 1898 the Library of Congress established Library of Congress Subject Headings (LCSH) to catalog materials held at the Library of Congress. This became the most widely used library classification system worldwide.
"By virtue of cooperative cataloging other libraries around the United States also use LCSH to provide subject access to their collections. In addition LCSH is used internationally, often in translation. LCSH in this service includes all Library of Congress Subject Headings, free-floating subdivisions (topical and form), Genre/Form headings, Children's (AC) headings, and validation strings* for which authority records have been created. The content includes a few name headings (personal and corporate), such as William Shakespeare, Jesus Christ, and Harvard University, and geographic headings that are added to LCSH as they are needed to establish subdivisions, provide a pattern for subdivision practice, or provide reference structure for other terms. This content is expanded beyond the print issue of LCSH (the "red books") with inclusion of validation strings" (http://id.loc.gov/authorities/subjects, accessed 08-21-2016).