"Treehouse of Horror XII" is the first episode of the thirteenth season of the American animated television series The Simpsons. Because of Fox's contract with Major League Baseball's World Series, the episode first aired on the Fox network in the United States on November 6, 2001, nearly one week after Halloween. It is the twelfth annual Treehouse of Horror episode, consisting of three self-contained segments. In the first segment, a gypsy puts a curse on Homer, which puts everybody he cares about in danger. In the second segment, which is a parody on both 2001: A Space Odyssey and Demon Seed, the Simpson family buys a new house, who falls in love with Marge and attempts to kill Homer. In the third and final segment, which lampoons the Harry Potter franchise, Lord Montymort attempts to capture Lisa, a skilled magician, in order to drain her magic powers.

The thirteenth season of the American animated television series The Simpsons originally aired on the Fox network between November 6, 2001, and May 22, 2002, and consists of 22 episodes. The showrunner for the thirteenth production season was Al Jean, who executive-produced 17 episodes. Mike Scully executive-produced the remaining five, which were all hold-overs that were produced for the previous season. The Simpsons is an animated series about an American family, which consists of Homer, Marge, Bart, Lisa, and Maggie. The show is set in the fictional city of Springfield, and lampoons American culture, society, television and many aspects of the human condition. This is also the last full season to use cel animation, though four episodes from this season's production cycle would air during the following season as holdover episodes.