The Worm Ouroboros is a heroic high fantasy novel by Eric Rücker Eddison, first published in 1922. The book describes the protracted war between the domineering King Gorice of Witchland and the Lords of Demonland in an imaginary world that appears mainly medieval and partly reminiscent of Norse sagas. The work is slightly related to Eddison's later Zimiamvian Trilogy, and collectively they are sometimes referred to as the Zimiamvian series.

Eric Rücker Eddison (24 November 1882 – 18 August 1945) was an English civil servant and author, writing under the name "E.R. Eddison". Eddison is best known for the early romance The Worm Ouroboros (1922) and for three volumes set in the imaginary world Zimiamvia, known as the Zimiamvian Trilogy: Mistress of Mistresses (1935), A Fish Dinner in Memison (1941), and The Mezentian Gate (1958).