At the Mountains of Madness is a science fiction-horror novella by American author H. P. Lovecraft, written in February/March 1931 and rejected that year by Weird Tales editor Farnsworth Wright on the grounds of its length. It was originally serialized in the February, March, and April 1936 issues of Astounding Stories. It has been reproduced in numerous collections.

The story details the events of a disastrous expedition to the Antarctic continent in September 1930, and what was found there by a group of explorers led by the narrator, Dr. William Dyer of Miskatonic University. Throughout the story, Dyer details a series of previously untold events in the hope of deterring another group of explorers who wish to return to the continent.