The Book of Eibon is a fictional grimoire created by Clark Ashton Smith, purportedly written by Eibon, the greatest wizard of prehistoric Hyperborea. It records his journeys to alien dimensions, his dealings with the toad-god Tsathoggua, and various forbidden rites.
Lovecraft and Derleth both incorporated it into their fiction, elevating it to a canonical forbidden tome comparable to the Necronomicon. It is known in Latin as the Liber Ivonis.