WorldCat is a union catalog that lists the collections of 17,900 libraries in 123 countries and territories that participate in the Online Computer Library Center (OCLC) global cooperative. It is operated by OCLC, Inc. The subscribing member libraries work together to maintain WorldCat's database. It is the world's largest bibliographic database. OCLC makes WorldCat itself available for free to libraries, but the catalog is also used for other subscription OCLC services (such as resource sharing and collection management). WorldCat is used by the general public and by librarians for cataloging and research.