The Three Impostors; or, The Transmutations is an episodic horror novel by British writer Arthur Machen, first published in 1895 in The Bodley Head's Keynotes Series. It was revived in paperback by Ballantine Books as the forty-eighth volume of the Ballantine Adult Fantasy series in June 1972.

Arthur Machen was the pen-name of Arthur Llewellyn Jones, a Welsh author and mystic of the 1890s and early 20th century. He is best known for his influential supernatural, fantasy, and horror fiction. His novella The Great God Pan has garnered a reputation as a classic of horror, with Stephen King describing it as "Maybe the best [horror story] in the English language." He is also well known for "The Bowmen", a short story that was widely read as fact, creating the legend of the Angels of Mons.