WorldCat

WorldCat is a union catalog which itemizes the collections of 72,000 libraries in 170 countries and territories which participate in the Online Computer Library Center (OCLC) global cooperative. It is built and maintained collectively by the participating libraries.

History
Created in 1971, it contains more than 246 million different records pointing to over 1.77 billion physical and digital assets in more than 470 languages. It is the world's largest bibliographic database. OCLC makes WorldCat itself available free to libraries, but the catalog is the foundation for other fee-based OCLC services (such as resource sharing and collection management). WorldCat was founded by Fred Kilgour in 1967.

In 2003, OCLC began the "Open WorldCat" pilot program, making abbreviated records from a subset of WorldCat available to partner Web sites and booksellers, to increase the accessibility of its member libraries’ collections. In 2006, it became possible to search WorldCat directly at its website. In 2007, WorldCat Identities began providing pages for 20 million "identities", predominantly authors and persons who are the subjects of published titles.

Limitations
Eastern European and Eurasian library holdings are not well-represented in the system.

WorldCat operates on a batch processing model rather than a real-time model. That is, WorldCat records are synchronized only at intermittent intervals with the underlying library catalogs instead of real-time or even every day. WorldCat merely shows that a particular item is listed in the catalog of a library, but cannot indicate if the item has been borrowed and is therefore unavailable for access by other patrons right now. As a partial workaround, WorldCat allows participating institutions to add direct links to WorldCat to their catalog entries for a particular item, but this is not as convenient as being able to view current status for all institutions owning an item on a single Web page.