OCLC

OCLC, Inc. is a library service and research organization. It helps people find more information and helps libraries work. It was started on July 6, 1967 as the not-for-profit Ohio College Library Center. Later its name changed to Online Computer Library Center as it grew. In 2017, its name changed to OCLC, Inc. 30,000+ libraries in 100+ countries are members of OCLC. The organization was started by Fred Kilgour. Its head office is in Dublin, Ohio, U.S.A. It makes WorldCat, a very big online catalog (a list of books and things like books).
OCLC control numbers.
OCLC gives a special number (called "OCN" for "OCLC Control Number") to every new record in WorldCat. A record is metadata about books and things like books. Every record has a different number. There are more than a billion numbers, and there are more every day. Old numbers are small and new numbers are big.
OCNs help find books and things like books that do not have ISBNs. Many books from before 1970 do not have ISBNs. OCNs are often used for books in Wikipedia and Wikidata.