1. Local to Global:
Start with the WashU Catalog, then to see a larger collection, try the MOBIUS Catalog, and then, to see what's available in libraries world-wide, check the WorldCat Catalog.
2. Or...Start Global:
WorldCat does show what titles are held locally at WashU. So, by starting in WorldCat, you can see a large view as well as find out what is here.
3. And another option...
4. And one more:
Depending on what you're looking for you might also search the Center For Research Libraries Catalog and HathiTrust (Note: searches in Primo does include HathiTrust.
Borrowing from WU and through Interlibrary Loan (ILL)