Encyclopedia Cthulhiana is a reference guide to the invented places, beings, and concepts from the Cthulhu Mythos developed by H. P. Lovecraft and others.

[2]: 435 Encyclopedia Cthulhiana is a 400-page book by Daniel Harms that contains an alphabetized listing of entities, cults and lore from H.P.

Sources include works by Ramsey Campbell, Robert Bloch, and Stephen King, as well as scenarios from the Call of Cthulhu game.

There are also suggestions about how this information could be included in a Call of Cthulhu adventure or campaign.

[2]: 436 In Dragon magazine #218 (June 1995), Rick Swan stated that this book possessed "a diligence on the part of the researchers that borders on the superhuman".