"Treehouse of Horror XVII" is the fourth episode of the eighteenth season of the American animated television series The Simpsons, and the seventeenth Treehouse of Horror episode. It originally aired on the Fox network in the United States on November 5, 2006. In "Married to the Blob", Homer eats green extraterrestrial slime and morphs into a rampaging blob with an insatiable appetite; in "You Gotta Know When to Golem", Bart uses Krusty's golem to wreak havoc on his tormentors; and in "The Day the Earth Looked Stupid", the residents of a late-1930s Springfield refuse to believe news of an actual alien invasion after being duped by Orson Welles's The War of the Worlds radio broadcast.

Treehouse of Horror is a series of annual Halloween-themed anthology episodes of the animated sitcom The Simpsons. Also known as The Simpsons Halloween Specials, each episode typically consists of three separate, self-contained segments. Each segment involves the Simpson family in some comical horror, science fiction, or supernatural setting; plot elements operate beyond the show's normal continuity, with segments exaggeratedly more morbid and violent than a typical Simpsons episode. With 34 episodes as of 2023, each Treehouse of Horror episode is numbered in Roman numerals, one less than the respective season it is in.