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 33 episodes as of 2022, each Treehouse of Horror episode is numbered in Roman numerals, one less than the respective season it is in.
The eponymous first installment "Treehouse of Horror" aired on October 25, 1990, during the second season, broadly inspired by EC Comics horror tales. In addition to parodies of horror, science fiction, and fantasy films, episodes include the recurring alien characters Kang and Kodos, unique opening sequences, and 'scary' pseudonyms in the credits. Treehouse of Horror episodes have earned high ratings and broad popularity, spawning a steady stream of merchandise, including a comic book series that ran from 1995 to 2017.
Segments
Treehouse of Horror episodes typically consist of four parts: an opening and Halloween-themed version of the credits, followed by three segments. These segments usually have a horror, science fiction or fantasy theme and quite often are parodies of films, novels, plays, television shows, Twilight Zone episodes, or old issues of EC Comics. Although they are sometimes connected by "wraparounds", the three segments rarely have any kind of continuing connection within the episode. Some have recurring elements, such as "Treehouse of Horror V", in which Groundskeeper Willie is killed by an axe in all three segments. The episodes are considered to be non-canon, which means they take place outside the normal continuity of the show.
The number of episodes of Treehouse of Horrors matches the number of series of the show: there are no such specials in season 1, two in season 34 and one in each other season. From "Treehouse of Horror" to "Treehouse of Horror XIII" and resuming with "Treehouse of Horror XXXIII", all three segments were written by different writers. In some cases there was a fourth writer who wrote the opening and wraparound segments. For the original "Treehouse of Horror", there were three different directors for the episode. From season 15's "Treehouse of Horror XIV" to season 33's "Treehouse of Horror XXXII", however, only one writer was credited with writing each Treehouse of Horror episode. "Treehouse of Horror XXXII" featured five segments. One of the season 34 Treehouse of Horror specials, "Not It", is distinguished by its uncharacteristic title and one full-length segment (divided in the two parts).
On occasion, the episodes will be used to showcase special animation, such as the "Treehouse of Horror VI" segment "Homer3", in which a computer-animated Homer is shown in a non-animated setting. At the time (1995), it was unusual for a television show to use such animation. The segment was executive producer Bill Oakley's idea and included live-action directed by David Mirkin. "Treehouse of Horror XX" included the segment "There's No Business Like Moe Business", which was the first to be musically themed.
Traditions
Opening sequence
The first, second, and fifth Treehouse of Horror episodes open with Marge standing on a stage and warning parents about the content of the episode, advising them to put their children to bed. The warning in the first episode was put in as a sincere effort to warn young viewers, as the producers felt it was somewhat scary. The entire segment was a parody of Edward Van Sloan's pre-credits warning from the 1931 film Frankenstein. Marge's warnings quickly became a burden to write, particularly because – as she herself noted – they were mostly ignored, so after "Treehouse of Horror V", they were dropped. The segment returned in the season 31 episode "Thanksgiving of Horror".