The Library of Congress Control Number (LCCN) is a serially-based system of numbering cataloging records in the Library of Congress in the United States. It has nothing to do with the contents of any book, and should not be confused with Library of Congress Classification. The LCCN numbering system has been in use since 1898, at which time the acronym LCCN originally stood for Library of Congress Card Number. It has also been called the Library of Congress Catalog Card Number, among other names. The Library of Congress prepared cards of bibliographic information for their library catalog and would sell duplicate sets of the cards to other libraries for use in their catalogs. This is known as centralized cataloging. Each set of cards was given a serial number to help identify it.