At the Mountains of Madness is a novella by horror writer H. P. Lovecraft, written in February/March 1931 and originally serialized in the February, March and April 1936 issues of Astounding Stories. It has been reproduced in numerous collections since Lovecraft's death.

Lovecraft scholar S. T. Joshi describes the novella as representing the decisive "demythology" of the Cthulhu Mythos by reinterpreting Lovecraft's earlier supernatural stories in a science fiction paradigm.