First, the FamilySearch Catalog. This is now a compilation of all of the holdings of all of the larger FamilySearch Centers around the world. Here is a screen shot of the link showing some of the FamilySearch Centers now being integrated into the master catalog:
First you click on the link that says "Search these Family History Centers:"
When you click, you get a list of all of the participating Centers. Any search you make will include all of the Centers. There is a further link on any resulting search window taking you to any Center having a copy of the item you are searching for:
Note that there is also a link to the digitized copy of the book, free and online, if one exists. Clicking on the link to the "Location" gives you a drop-down list of all of the FamilySearch Centers that have a copy of the item.
Now, if you look near the bottom of this same search page, you will also see a link taking you directly to the WorldCal.com (OCLC) catalog website:
Clicking on this link takes you directly to the catalog entry in the WorldCat.org catalog:
Notice that there are entries for the Family History Library and for the Mesa Arizona FamilySearch Library. But you should also note all the other locations where this particular book can be found, including the previously noted online version.
Any genealogist worth their salt should be very well acquainted with WorldCat.org. With over 2 billion catalog entries, this is the most valuable searching resource for genealogists on the Internet after Google. If you use WorldCat.org regularly, you just might begin to understand why this linking of the two catalogs is so important.
See "FamilySearch Catalog Will Soon Link to the OCLC World Catalog" on the FamilySearch.org blog for another announcement.