The Treehouse of Horror series, formerly known as The Simpsons Halloween Specials, are an annual tradition in which there is a special Halloween episode consisting of three separate, self-contained pieces. These pieces usually involve the family in some horror, science fiction, or supernatural setting; they always take place outside the normal continuity of the show (and are therefore considered to be non-canon) and completely abandon any pretense of being realistic.
Regular Simpsons characters play humorous special roles, often being killed in gruesome ways by monsters or even each other. Groundskeeper Willie has died many times in the Treehouse of Horror episodes, mostly by being stuck in the back with an ax, impaled by a sharp object, burned by a furnace, and even once by a dolphin. The Halloween episodes also regularly parody many classic horror and science fiction films and episodes such as The Shining, "Nightmare at 20,000 Feet", "To Serve Man", "Living Doll", "It's a Good Life", "A Kind of a Stopwatch", "The Little People", "Little Girl Lost", Twilight, 28 Days Later, and others.
According to some DVD commentary, the reason why the episodes are non-canon is a trade-off for the writers. Writing three 7-minute segments was just too taxing for the writers, so it was proposed that they could do anything without worrying about continuity to appease them.
The yearly Halloween special was named "Treehouse of Horror" because the original special depicted the Simpson children in their treehouse telling scary stories to one another. In later years, the series dropped the framing device of characters telling stories but kept the Treehouse title. It also takes reference from a classic horror movie Dr. Terror House of Horrors which was an anthology of six different horror stories.
In a section of "Treehouse of Horror VI" called "Homer³," Homer and Bart go into a three-dimensional world, which Homer likens to Tron, created by Pacific Data Images, a computer animation company that would later produce Shrek. This segment from the Halloween episode was also used as a segment of a film shown in the IMAX 3D film Cyberworld. This was the first and one of the few times the Simpsons have strayed from their traditional 2D animation, and the longest, as other moments consisted of live action couch gags or short claymation or CGI television and film parodies. Other Treehouse segment name parodies include "Citizen Kang" (Citizen Kane), "Nightmare on Evergreen Terrace" (Nightmare on Elm Street), "The Thing and I" (The Thing and also The King and I), "Hex and the City" (Sex and the City), "House of Whacks" (House of Wax), "I've Grown a Costume on Your Face", "The Ned Zone" (The Dead Zone), "The Shinning" (The Shining) and "Reaper Madness".
For several years, the characters broke the fourth wall and introduced their three stories directly to the audience. In "Treehouse of Horror II" the writers decided to give the cast and crew of the show 'scary names' in the opening and closing credits (like "Bat Groening" and "James Hell Brooks"). This also became a classic tradition and has been done in every Halloween episode since Treehouse of Horror except for Treehouse of Horror XII and Treehouse of Horror XIII. Their names have changed in subsequent seasons, with the exception of Sam Simon's, who left during the fourth season. Sam has since (with the exception of Treehouse of Horror XXII and Treehouse of Horror XXIII) remained "Sam 'Sayonara' Simon."
Another mainstay of the Halloween shows is the yearly appearance of the two space aliens Kang and Kodos, introduced in the second segment of the first "Treehouse of Horror" episode. However they are not always important to any story in the special; starting with "Treehouse of Horror III" they began appearing just to keep up with the tradition. While they have had significant parts in other "Treehouse of Horror" episodes, they often only appear in the middle of a completely different story, for example, a story about zombies attacking the town will suddenly switch to them watching in outer space, watching all the events and laughing maniacally at the Earthlings' suffering, before switching back to the actual story. In much later years Kang and Kodos would sometimes appear at either the beginning or end of the episode, outside of any of the stories; for example, one year they appeared between the last segment and the credits wondering "Why The Simpsons producers hadn't called us to be in this episode?". Soon they get a call offering them to be on a commercial for something called "Old Navy".
From the 2nd Halloween special onwards, the Gracie Films logo (excluding VI and XIX), there is a pipe organ playing the jingle and a girl screaming loudly in the background (which sounds more like a whistle), in II and III, the organ played without the scream, on IV, the scream was added in. The scream was replaced with other quotes or Homer's screams. On IX, the organ played, but the scream was replaced with Regis Philbin screaming, "My eyes, my beautiful eyes!". On XV, the scream was replaced with Homer screaming loudly through this logo and 20th Century Fox Television logo, similar to The Blunder Years. On XXIV, the scream was replaced with the mob saying "One of us!". On XXVI, the scream was replaced with Homer-zilla's roar.
Also, at the start of Treehouse of Horror I, II, and V, Marge (or Homer in III) comes out with a message urging the parents not to let their children watch the Halloween episodes as they will all suffer from nightmares; however she soon gives up, saying that none ever listens to her. This was abandoned in later seasons, because the length of each episode has been reduced significantly since the first few seasons, and also because the current writers were sure that everyone was aware that the Halloween episodes were scary by then, and its also probably because it was too boring.
Another tradition that the writers abandoned was including old tombstones with humorous messages (along with poking fun at the paul is dead rumour) in the opening credits: the credits for Treehouse of Horror V included a single tombstone with the words "Amusing Tombstones" to signal this.
All of the Halloween Specials are officially named Treehouse of Horror, but the Halloween specials from Treehouse of Horror to Treehouse of Horror XII were dubbed The Simpsons Halloween Special. The name "Treehouse of Horror" was not given until the airing of Treehouse of Horror XIII.
The ending credits of Treehouse of Horror I, II, and III featured a cell from the episode (ideally a graveyard scene) during the end credits to which was changed in Treehouse of Horror IV but used again in Treehouse of Horror XV. As well as including a spooky version of The Simpsons theme song in every episode, with some exceptions. The Halloween ending credits theme then evolved to become a brief medley of the episodes musical scores.
Although the Treehouse of Horror series is meant to be seen on Halloween, in recent years new installments have premiered after or before Halloween. This is due to Fox's current contract with Major League Baseball's World Series and Playoff games. If the Series does not go the full seven games, Fox usually airs the previous season's Treehouse of Horror episode on the Sunday before Halloween. However, it has been known on many occasions for new shows to premiere on the West Coast only in time for Halloween regardless of how long the World Series lasts. It gets the full national premiere, of course, as scheduled in November, after Halloween. Another reason for the late airing is that during November, Nielsen Media Research conducts one of its four annual sweeps months - in recent years, the annual Treehouse of Horror episodes tend to draw some of the highest ratings of the season to which it belongs. Between Treehouse of Horror XI to Treehouse of Horror XIX and Treehouse of Horror XXI was aired in November.
FOX's arrangement with Major League Baseball was made fun of in the opening sequence for "Treehouse of Horror XVI". Kang, frustrated that the episode is being delayed by a World Series baseball game, decides to "fast forward" the game, but overdoes it, sucking the Earth, the universe, and everything else (including God) into nothingness. He then leaves a sticky note, which shows the title. Another joke about the programming of Halloween episodes in November appears in "Treehouse of Horror XIV", where Kang looks at a TV Guide and says, "Those humans. They're showing a Halloween episode. In November!" Kodos replies, "Who cares about Halloween? We've already got our Christmas decorations up!" The camera then cuts to a shot of the fireplace with Christmas decorations, complete with multi-legged stockings and alien reindeer, scattered about, and festive Christmas music plays over the opening credits.
So far, only four Treehouse of Horror episodes were aired before the World Series: Treehouse of Horror XX, Treehouse of Horror XXIII, Treehouse of Horror XXIV and Treehouse of Horror XXVII. Every other Treehouse of Horror episodes were aired right after the World Series with half of them going into November.
The opening sequences in recent years have been longer than the original openings, almost being a fourth segment. They would feature a short story with Kang and Kodos (Treehouse of Horror XV, Treehouse of Horror XVI) feature the Simpson family feuding, (Treehouse of Horror XIV) or might include a character talking to the audience about the show. (Treehouse of Horror XVII, Treehouse of Horror XXI)
In 1995, Matt Groening's Bongo Comics Group, a company specializing in Simpsons-based publications, began a series of comic book adaptations of the Treehouse of Horror series. These annual editions are released in September each year, and as of September 2007 there will be thirteen issues available. Originally, guest writers from other comic book companies were invited to submit scripts to Bongo, where the comics themselves would then be drawn by Bongo staff. Beginning with #5 (1999), the "guests" were allowed to submit both stories and art, wherein at the most Bongo would only supply the lettering and coloruings of the stories. However, there are few cases of this rule being broken; i.e., "The Catastrophe on Substitute Springfields" (#7, 2001) and "The Legend of Batterface" (#10, 2004). The comics were also more surreal than the episodes, with more gore, and more scary scenarios than the show would do.
- THOH – "Treehouse of Horror"
- THOH – "Treehouse of Horror II"
- THOH – "Treehouse of Horror III"
- THOH – "Treehouse of Horror IV"
- THOH – "Treehouse of Horror V"
- THOH – "Treehouse of Horror VI"
- THOH – "Treehouse of Horror VII"
- THOH – "Treehouse of Horror VIII"
- THOH – "Treehouse of Horror IX"
- THOH – "Treehouse of Horror X"
- THOH – "Treehouse of Horror XI"
- THOH – "Treehouse of Horror XII"
- THOH – "Treehouse of Horror XIII"
- THOH – "Treehouse of Horror XIV"
- THOH – "Treehouse of Horror XV"
- THOH – "Treehouse of Horror XVI"
- THOH – "Treehouse of Horror XVII"
- THOH – "Treehouse of Horror XVIII"
- THOH – "Treehouse of Horror XIX"
- THOH – "Treehouse of Horror XX"
- THOH – "Treehouse of Horror XXI"
- THOH – "Treehouse of Horror XXII"
- THOH – "Treehouse of Horror XXIII"
- THOH – "Treehouse of Horror XXIV"
- THOH – "Treehouse of Horror XXV"
- THOH – "Treehouse of Horror XXVI"
- THOH – "Treehouse of Horror XXVII"
- THOH – "Treehouse of Horror XXVIII"
- THOH – "Treehouse of Horror XXIX"
- THOH – "Treehouse of Horror XXX"
- THOH – "Treehouse of Horror XXXI" (upcoming)
- THOH – "Treehouse of Horror XXXII" (upcoming)
- THOH – "Treehouse of Horror XXXIII" (upcoming)
- THOH – "Treehouse of Horror XXXIV" (upcoming)
- THOH – "Treehouse of Horror XXXV" (upcoming)