WorldCat is the world's largest network of library content and services. WorldCat libraries are dedicated to providing access to their resources on the Web, where most people start their search for information.

WorldCat.org lets you:

• Search many libraries at once for an item and then locate it in a library nearby
• Find books, music, and videos to check out
• Find research articles and digital items (like audiobooks) that can be directly viewed or downloaded
• Link to "Ask a Librarian" and other services at your library
• Post your review of an item, or contribute factual information about it

What am I searching?

WorldCat.org lets you search the collections of libraries in your community and thousands more around the world. WorldCat grows every day thanks to the efforts of librarians and other information professionals.

What will I find?

You can search for popular books, music CDs and videos—all of the physical items you're used to getting from libraries. You can also discover many new kinds of digital content, such as downloadable audiobooks. You may also find article citations with links to their full text; authoritative research materials, such as documents and photos of local or historic significance; and digital versions of rare items that aren't available to the public. Because WorldCat libraries serve diverse communities in dozens of countries, resources are available in many languages.

Can I check something out?

It depends on whether you have an active membership with a library that owns the item, and whether that library's Web site permits remote checkout of an item. WorldCat.org lets you find an item of interest and then locate a library near you that owns it. Usually you will link directly to the item record on the library's Web site. The actions available to you on that page will vary from one library to another. You may be able to join a waiting list, reserve the item, check it out or even have it shipped or delivered.

Can I get into electronic databases?

Some WorldCat libraries make their specialized reference databases available on their Web sites, but only to library members. Your search on WorldCat.org may produce direct links to articles and other resources in these databases. To access these resources, though, you may first be required to log in with a valid library membership.

http://www.worldcat.org/whatis/default.jsp

WorldCat versus HathiTrust

WorldCat is different from HathiTrust in a few major ways. 

• Both resources are comprised of a network of libraries coming together to provide valuable access to electronic and in-print information in all formats.
  
• HathiTrust, however, is more like a library in that it is a repository for digital content such as ebooks. 
• WorldCat is not a repository, it is a huge online catalog capable of accessing thousands of library catalogs at once. 
• HathiTrust holds about 10 million volumes of digital content, while WorldCat provides access to over 1.5 billion items in libraries world-wide. 
• One of the biggest advantages about the records you search in WorldCat is that they can be very detailed and thorough. 
• Searching by the title of a chapter or character in a play might bring back the result you are looking for in WorldCat, but not in HathiTrust or even Orbis.

Therefore, the two resources should both be used for your research.  There is even this WorldCat-HathiTrust prototype catalog that will allow you to take advantage of both online resources.