"The Transition of Juan Romero" is a short story by American horror fiction writer H. P. Lovecraft, written on September 16, 1919, and first published in the 1944 Arkham House volume Marginalia.

The night after the discovery of the abyss the narrator and one of the mine's workers, a Mexican called Juan Romero, venture together inside the mine, drawn against their will by a mysterious rhythmical throbbing in the ground.

The story was a private illustrative exercise, meant only for the eyes of his small circle of correspondents.

Written in less than a day, it was meant to quickly demonstrate what might be done with a desert setting that had been used in what Lovecraft called a "dull yarn" of a story (now lost) by 'Phil Mac' (Prof. Philip Bayaud McDonald).

[2] Lovecraft seems to have disavowed the story early in his writing career.