OCLC’s WorldCat approaches 475 million bibliographic records. Many of those records have been created manually by members of OCLC’s worldwide cooperative. Others have been added to WorldCat en masse from institutions large and small, from national libraries, from cultural heritage institutions, or from rural public libraries.
Resource Description and Access (RDA), the successor to the Anglo-American Cataloging Rules (AACR), has had a significant impact on both bibliographic and authority data as they are represented in Machine-Readable Cataloging records in MARC 21. A brief history of the develoment of RDA is outlined. Since 2006, OCLC has kept up with some fifteen MARC 21 Bibliographic, Authority, and Holdings Updates through a total of nine OCLC-MARC Updates.