Who's Who and What's That is an ongoing series of books that appears to serve as a listing of known supernatural entities.
The latest volume of "Who's Who and What's That" was checked out from the New York City Public Library by Cubby. In combination with "Spirit Summonings and Conjurations" and "Lochmore's Guide to the Lower Regions," he was able to cast a Class 5 Summoning. A copy of "Who's Who and What's That" was later purchased by Egon Spengler. It was stored in the Firehouse's library in the second bookcase, on the third shelf, and in the dead center. Egon used it while trying to match up an entity with the description Lee Meredith gave of one corrupting his brother.
- On page 11 of Ghostbusters Issue #15, "Who's Who and What's That" makes a non-canon cameo in the arms of Alice.
- Egon Spengler (2009). The Real Ghostbusters - "The Grundel" (1987) (DVD ts. 13:38-13:39). Time Life Entertainment. Egon says: "Have you seen my copy of Who's Who and What's That?"
- Janine Melnitz (2009). The Real Ghostbusters - "The Grundel" (1987) (DVD ts. 13:40-13:44). Time Life Entertainment. Janine says: "Library. Second bookcase. Third shelf. Dead center."