This article is about the fictional depiction of sexual activity between two or more characters who are closely related by kinship.
Prevalence in Fandom
In some fandoms, incest fic involving a specific pair of characters is relatively common. In Supernatural, many stories are written about the brothers Sam and Dean; some stories include one or both men and their father. In Harry Potter, stories about sexual relations between the Weasley twins are very common, and sometimes tolerated even by people who refuse to read any other incest fic. Stories about Draco and Lucius Malfoy or the Black family are also fairly common. In the late '80s - early '90s, Simon & Simon slash between the two Simon brothers was not uncommon, though fairly stigmatized at the time. In the late 1990s Kung Fu: The Legend Continues had a mailing list dedicated to the intergenerational father/son incest pairing of the fandom, i.e. Peter/Pop slash.
Incest is also common in some RPF fandoms. Lord of the Rings actor Elijah Wood is sometimes paired with his sister Hannah, and Gerard Way/Mikey Way is one of the most popular My Chemical Romance pairings.
- Brothercest or brotherslash for the incestuous relationship between brothers.
- Daddycest for the incestuous relationship between a character and his or her father.
- Siblingcest or sibcest for the incestuous relationship between siblings.
- Twincest is the incestuous relationship between twins.
- Wincest is another term for incest or twincest, e.g. "incest is wincest" (to describe something as "win" is to call it a good thing). It is also a term for an incestuous relationship between the Winchester brothers in Supernatural fandom.
- Clonecest (more extensively described on the doppelganger page) is used for literal clones or for characters multiplied via alternate universes, time travel, magic, replication superpowers, etc. Also used in some fandoms for crossovers pairing characters played by the same actor.
To name pairings, "cest" can be added to the end of the characters' last name, or a shortened form of their last name, e.g. Winchester becomes Wincest, Uchiha becomes Uchihacest, Petrelli becomes Petrellicest, Tam becomes Tamcest, and so forth. The "cest" ending can be added to a number of words to show an incestuous scenario or kink, as noted in the terms listed above.
Fandoms with significant incest pairings
This section has just started -- please fill it in.
Any fandom can have a one-off story. These are sources where one or more incest pairings are common in stories/vids/art of the fandom.
- Batman -- "Batcest" or "Robincest"
- Digimon -- Brothers Yamato and Takeru, and Osamu and Ken were sometimes paired, as well as Taichi with his sister Hikari
- Firefly -- "Tamcest" or "Crazy Space Incest" Simon/River
- Harry Potter -- many common incest pairings: Weasley and Patil twincest, plus frequent pairings in the Black, Malfoy, and Weasley families.
- Hetalia -- Many countries are siblings or parent/child and are paired together. Among the most popular yaoi couples are US/UK, though this pair is not always written as an incest couple. Also Germancest (Germany/Prussia) and the het couples Switzerland/Lichtenstein and Belarus/Russia. The latter has canon support.
- Heroes -- "Petrellicest" Nathan/Peter, Peter/Claire
- InuYasha -- "Inucest", half-brothers Inuyasha/Sesshoumaru are the mainly shipped incest pairings. Less popular is the Inu no Taisho/Sesshoumaru, father/son, and Inu no Taisho/Inuyasha, father/son. On rare occasion, there is the Sango/Kohaku pairing, brother sister.
- Kung Fu: The Legend Continues
- Lord of the Rings -- Eowyn/Eomer, Boromir/Faramir
- Lost -- Pacecest
- Loveless -- Seimei x Ritsuka
- Narnia -- Pevensiecest
- Naruto -- "Uchihacest" especially Itachi/Sasuke, Hyuugacest specifically Neji x Hinata
- Numb3rs -- "Eppecest" Don/Charlie
- Revolutionary Girl Utena -- Anthy/Akio, Miki/Kozue, and Touga/Nanami, all of which are suggested in canon
- Sherlock (BBC) -- "Holmescest" Sherlock/Mycroft
- Simon & Simon -- Incest from the slash early days.
- Smallville -- "Luthorcest"
- Supernatural -- "Wincest" Sam/Dean are probably the biggest incest pairing, ever; Dean or Sam are also paired with their father, John, or sometimes their mother, Mary
- Teenage Mutant Ninja Turtles -- The turtles have been raised as brothers in all incarnations of the story, though whether they are genetically related is usually unknown; all the turtles have been paired together at some point, but Leonardo/Raphael is the most common.
- The Vampire Diaries -- "Salvatoreslash" the sibling incest ship between Damon and Stefan Salvatore is popular in both the book and tv series fandoms.
- Vampire Knight -- Various incest ships in canon as well as fanon, including twincest.
- Bandom -- Waycest (My Chemical Romance)
- Popslash -- Lynncest (NSYNC), Cartercest (Backstreet Boys), Jonas Brothers, Hanson
- LoTRiPS -- Woodcest Elijah/Hannah Wood
See the list of twincest pairings in the twincest article.
As incest has been a powerful taboo in most societies throughout most of history (although societies have varied in their definition of kinship), controversy is bound to arise over the fictional depiction of incest in fanworks.
Many fans refuse to read any of it, and believe all of it is sick and wrong.  Others see incest fiction as normalizing abuse and sexual assault and believe that repeated exposure to the genre and its greater acceptance in fandom creates an atmosphere whre the abuse becomes tolerated in real life. Still, some objectors are willing to allow themes of incest within fandom providing they are not written to satisfy kink and do not whitewash abuse. 
Same vs. Cross-Generation
Others can accept incest fic among peers (siblings, esp. adult siblings) but not cross-generational incest such as parent/child:
I would like to state that I am a fan of incest pairings, and a fan of Gerard/Mikey in general. ... But my interest lies solely in fics featuring explicit consent and mutual desire. I also believe that abuse, pedophilia, rape, and assault are all valid fictional topics, but they must be framed in an examining, empowering, or at the very least artistic context. This fic does none of those things, and I will allow for the possibility that the author intended for those things to be included, but personally I don't see a single shred of it.
Did I mention that I draw the line at RPS twincest? Actually, not only do I draw the line but, like Harold with his Purple Crayon, the line itself becomes a fucking huge wall that's got a door and the door has got a couple of thousand heavy duty locks on it. Like, remember the wall with the door that kept King Kong out on Skull Island? That one, but twice as tall and reinforced with a great, big NO on it.
Slash vs. Het
There is a common perception in many fandoms that slash incest pairings are much more accepted than heterosexual ones. Complaints and discussions of this pattern regularly turn up in anonymous forums like LOL meme and fandomsecrets. This same pattern has been observed outside of fandom as well.
What's the appeal? Why do fans read/write/draw/vid/etc. incestuous pairings? Sometimes it's because of the taboo, sometimes it's in spite of it, and sometimes the taboo is irrelevant.There are many fans for whom incest pairings have a special appeal. Sistermagpie says about the attraction of brother/sister incest for her:
It's not about abuse it's about...finding your other half, I suppose. The yin-yang, the reciprocal self, the male version of the female self (I've not much thought about it from the other way round...I always made the girl the rescuer, I think). Unlike parent/child incest, it's not about power because the whole point is that the two people are completely evenly matched. They need each other. Explanations or justifications for including incest in a story can include:
- "No matter whether their canonical relationship is brotherly, these characters/actors are way hot and I want to envision them getting together!"
- "Those guys are showing some major subtext between them! They practically beg to be slashed!" (and given that slashy friends often say they love each other "like a brother" the conflation of family intimacy and sexual intimacy as types of emotional intimacy is a common cultural concept)
- "I've got a brocest kink already, and these guys give me a great excuse to air it out!"
What that means is, the sibling incest angle is neither a squick nor part of the attraction for me. It's a fact of that particular slash pairing that I have to deal with as a writer the same way I have to deal with them being two basically straight guys (as depicted on my television). It makes the pairing interesting for me in pretty much the same way that taking two basically straight guys and getting them together in a sexual/emotional relationship makes slash interesting to me. But I'd still be writing Sam/Dean slash if one of them were adopted or something, or if they were second cousins, or whatever. Incest is a factor; but it's not the defining factor for me. 
Evolution in fannish works that include incest
Some fans argue that as incest pairings have become more common in fanworks, that the way 'cest pairings are being written has changed. For example, Zvi said in her DW account, "cheery, uncomplicated, happily ever incest ... is new and strange." Initially most or all 'cest stories made at least a nod to the fact that they were doing something considered wrong by society. More recently, though there are still plenty of angsty 'cest stories, many stories ignore incest issues altogether -- somewhat like historical aus that allow same-sex marriage with no one blinking an eye.
Incest in Alternate Universes
Some fans do write AUs where the incestuous pairings are not related. This is a sub-genre in Supernatural.
Less common is the AU that takes an unrelated couple and turns them into an incestuous pairing. This is sometimes used for some ambiguously incestuous characters such as the Batfamily in DC Comics, where an AU might change it so characters were more closely raised together.
Season ten of Smallville introduced a canon AU where Clark Kent had been raised a Luthor and was sleeping with his sister Tess. However, fans had already been writing Clark/Lex Luthorcest AUs since a season two storyline that revealed Lionel's part in the Kents' adoption of Clark.
Canonical incest in Western fandoms
Some, usually minor, fannish sources feature canonical incest. Flowers in the Attic is probably the most mainstream example of incest between two biologically related siblings who were raised together. Another is Wiseguy: Mel and Susan Profitt, a brother and sister raised together, have a clearly implied relationship in canon which is later made more explicit when another character, referring to Susan's pregnancy, notes that the baby could very well be Mel's. In Blades of Glory, US figure skating pairs team of brother and sister Stranz and Fairchild Van Waldenberg share an off-rink intimacy that lends a certain piquancy to their routines.
A tragic intra-generational incestuous relationship, fatal for both siblings involved, is told by J.R.R. Tolkien in The Children of Húrin, where the wedded couple Turin and Nienor turn out to be brother and sister. Both commit suicide. It is set in the Middle Earth universe.
George R.R. Martin's fantasy series A Song of Ice and Fire and the TV show based on the books, Game of Thrones, includes brother-sister incest between Jaime and Cersei Lannister which results in three children who are believed to be children of (and thus heirs to) Cersei's husband, King Robert.
Robert A. Heinlein's World As Myth universe incorporated incest in several stories, both between siblings and between parent/child, particularly in the novel Time Enough for Love. In this universe, as long as the threat of a bad combination of recessive genes is averted, there's no incest taboo.
Sometimes the interaction between two characters in canon reads to the fans like romantic or sexual chemistry, but then TPTB reveal that the two characters are actually related, retconning the pairing to be incestuous. For instance, part of the plot of Veronica Mars, season 1, involves Veronica discovering that her ex-boyfriend Duncan may actually be her half-brother, causing Veronica to fear that she has unwittingly been in an incestuous relationship. Luckily, this turned out to be fakecest.
Similarly, in Heroes, several episodes after Peter and Claire met, viewers learned that he was actually her uncle. Rather than let their pairing be jossed, some fans continued to ship Peter/Claire anyway.
Star Wars is another well-known example: Leia kisses Luke on the cheek in Star Wars: A New Hope, on the mouth in The Empire Strikes Back, and is revealed to be his secret long-lost twin in Return of the Jedi, thus turning Luke/Leia into a rare het twincest pairing. Published in March of 1978, the first Star Wars tie-in novel, "Splinter of the Mind's Eye" by Alan Dean Foster, features several scenes with explicit sexual tension between Luke and Leia. 
Another canon pairing came to light in Marvel Comics' The Ultimates, written by Jeph Loeb. Previously, Wanda and Pietro's relationship had been a matter of subtext, but in issue #1 of the third Ultimates series, they were revealed to have had a canonical twincest relationship. 
Canonical incest in manga/anime fandoms
Incest or near-incest is a common theme in many manga and anime. Revolutionary Girl Utena features both heterosexual sibling incest and lesbian sibling incest; in Ceres: Celestial Legend, a brother and sister are possessed by the spirits of dead lovers; in Neon Genesis Evangelion, a teenage boy obsesses over a clone of his mother; Saiyuki features several heterosexual incest pairings, including a twin brother and sister as well as a mother and son; and then there's Marmalade Boy, about two couples who decide to get divorced, swap partners, and re-marry, turning their children (one couple has a teenage boy, the other has a teenage girl) into double-step-siblings. Hijinks ensue.
Canonical ambiguously incestuous pairings
Though the definition of "incest" at first seems quite clear and unambiguous, different cultures and time periods have radically different definitions for it, and the legal definition may differ from how people generally use the word in daily life. Moreover, some relationships may be seen as having incestuous overtones without involving incest in a literal sense. Examples of relationships that are often perceived differently in different contexts include those between first cousins, more distant cousins, relatives by marriage, and people with a foster or adoptive relationship.
Many pairings within the Batman comics universe fall under this umbrella; pairings between characters who are not related and were not raised together may still be labeled "Batcest" if they are part of the "Batfamily" centered around Bruce Wayne, including relationships between the various characters who have been Batman, Robin, or Batgirl. "Robincest" is the term for shipping Robins with each other.
Similarly, in The Royal Tenenbaums, two siblings who are only related by adoption have what is technically an incestuous relationship. In Lost, step-siblings Shannon Rutherford and Boone Carlyle appeared to have a tension-filled, typically bickering sibling relationship; it was later discovered that they had engaged in an intimate relationship at least once, and (it seemed implied) probably more than once.
A sexual attraction between step-siblings Greg and Marcia is played for laughs in the Brady Bunch movie A Very Brady Sequel.
British fandoms, especially if they are historical, may feature relationships between cousins, which to American fans can seem incestuous. For instance, in The Grand Sophy by Georgette Heyer, the romantic hero and heroine are first cousins.
Step-siblings or adopted siblings falling in love is a fairly common plot device in anime and manga as well.
In the Darkover novels by Marion Zimmer Bradley sworn friends refer to each other as brother and sister ("bredu" and "breda") and the main affectionate term used by same-sex lovers is an especially intimate inflection of the same word ("bredhyu" and "bredhya").
- WARNING: Possible Dolt Porn (formerly Fan Fiction) Discussion thread on TWOP
- See Hossgal's author's notes to "Mother of Horses."
- See Hossgal's author's notes to "Mother of Horses."
- Why I disapprove, and why I will be neither ashamed, nor silent. LJ post by redsambuca, 14 May 2008
- Some RPS Meta-Thinkiness by LJ user miriam_heddy, Jun 26 2008
- Sistermagpie. Incest! Posted 22 July 2004.
- Meta: Fandom - Slash - Incest - Wincest... by on_verra, 3 Mar 2008
- Merryish.Pondering the Sam/Dean thing. Posted 22 August 2007.
- For example, Last Will and Testament by Speranza is a very rare Stargate Atlantis story where the popular slash ship turn out to be brothers. Certainly rare enough that the author felt the need to apologize.
- Wookieepedia, Splinter of the Mind's Eye Last accessed October 10, 2008.
- Doop, Ultimates 3 #1: Pietro and Wanda December 7, 2007. Last accessed October 9, 2008.
- Lost, Season 1, Episode 13, "Hearts and Minds."