The following excerpt is from an article posted January 8, 2014 at ancestryinsider.blogspot.com
Nearly a year ago FamilySearch and OCLC announced a partnership to exchange services. Search results from the OCLC catalog, WorldCat.org, would include the holdings of the FamilySearch Salt Lake City Family History Library (FHL). Search results from the FamilySearch catalog (formerly the Family History Library Catalog) would included results from WorldCat.
FamilySearch catalog links to WorldCat and Archive Grid. I noticed several weeks ago that on the FamilySearch beta catalog search page FamilySearch had started showing links to OCLC’s WorldCat and Archive Grid websites.
Archive Grid is a research project by OCLC aimed at cataloging archival holdings. It includes entries from WorldCat as well as materials published on the Internet. (There’s a system called EAD tags that archives can use to make their archival finding aids discoverable on the Internet.) It currently catalogs over two million items from thousands of libraries, archives, museums, and historical societies.