WorldCat is a cooperatively-created catalog of materials held in more than 7,600 libraries in the United States and the rest of the world, including public, academic, state and national libraries; archives; and historical societies. These libraries have cataloged their regular collections as well as many special collections—including digitized materials—devoted to local history. This makes WorldCat a unique tool for your research into your heritage.
Because WorldCat is a "super" catalog of more than 1 billion library holdings representing 54 million items held in libraries, you can reduce the number of places you search to locate useful material. WorldCat complements tools such as the LDS Family History Library, Ancestry.com and ProQuest's HeritageQuest™.
You can get access to WorldCat in two different ways, through a library offering FirstSearch service through on-site public access and through WorldCat.org on the Internet. See the publication "WorldCat for genealogy, A Tutorial." Depending on which part of the Web site you believe, the WorldCat has information on to up to 69,000 libraries world wide. WorldCat provides information about the library materials and where available, links to digitized versions of the materials.
As an example a search under the term "Nephi Utah" produced this document located in the Brigham Young University Library:
Greenhalgh, Sadie H. Chronology of Nephi Branch, 1851-1868; Nephi Stake of Zion, 1868-1877; Juab Stake of Zion, 1877-1974; Nephi Utah Stake, Jan. 20, 1974. 1982.
One amazing thing about WorldCat is that when you do find a book or other item, the Web site gives you the distance in miles to libraries holding the material arranged from the closest to the most distance.
WorldCat can also be featured on your Facebook and other social networking accounts. You can use this FaceBook connection to build your own list of favorite books and other links. This is one of the truely amazing programs on the Web and any serious researcher, in any discipline, including genealogy should be familiar with it.