WorldCat

WorldCat is a combined online catalog describing the collections of many libraries. According to its website, WorldCat is the world's largest network of library content and services, with over 150 million different records pointing to over 1.4 billion physical and digital materials in more than 470 languages. WorldCat lets users search the collections of libraries in their community and around the world: books, CDs, videos, manuscript collections, research articles, physical and digital items, abstract and full text.

For genealogists, WorldCat has many uses. Researchers can search library holdings by title, subject, and author; locate the nearest repository where an item is housed; identify items to order through interlibrary loan; and assist in finding items available online. WorldCat is also a good place to find citations for materials used in documenting sources. WorldCat is now being expanded to catalog content on the Web, increasing the visibility of materials such as the historical photos and archival documents found in various museums and archives.