At the Mountains of Madness is a novella by horror writer H. P. Lovecraft.

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.

The novella's title is derived from a line in "The Hashish Man," a short story by fantasy writer Edward Plunkett, Lord Dunsany: "And we came at last to those ivory hills that are named the Mountains of Madness..."

The story has inadvertently popularized the concept of ancient astronauts, as well as Antarctica's place in the "ancient astronaut mythology".