Tie-in Novel

The tie-in novel is literature involving the characters of a TV series, film or other work and usually written by some author you've never heard of. Pretty much anything can have a tie-in novel. They're often compared to authorized Fanfic, in that they're usually not part of the main continuity, do things that would never be considered in the original, and are widely variant in quality. If a series is exceptionally popular, the tie-novels may have their own micro-continuity. If it's mega-popular, expect them to occupy their own Expanded Universe. Expect tie-in novels by the same author to refer to events in their other novels.

These novels are usually written in a very conservative style. You're unlikely to encounter one written in the style of Margaret Atwood or Marcel Proust.

These can be novelizations of episodes or "untelevised adventures".

See Novelization for a main continuity story retold in book form. For the reverse--going from a book to the big screen--see The Film of the Book. For a similar concept but with videogames, see Licensed Game.

Anime and Manga

 * Robotech: Jack Mckinney -- a pseudonym for Science Fiction authors James Luceno and Brian Daley -- wrote a series of novelizations of the composite adaptation, which continued into a version of the unproduced Sentinels sequel, and several original tie-ins. The novels are considered Fanon Discontinuity by many fans because of the additions made to the premise, such as inventing the "Thinking Cap" mental control system for the Humongous Mecha, as well as turning the Applied Phlebotinum, previously just a flower that somehow generates power, into a narcotic that somehow directs the destiny of the universe. Though no one ever outright said "He who controls the protoculture, controls the universe!"
 * Many anime have "Animanga" which are pretty much screenshots from the Anime with word bubbles.
 * The Magical Girl Lyrical Nanoha has a tie-in novel set after a slightly altered ending of the first season where, instead of Nanoha's winning against Fate in their battle, the fight ends without a conclusion since Precia interfered early, and Nanoha goes after Fate after Precia is killed so they can have a proper end to their duel. The novel, however, is official, written by the very creator of Nanoha. The background information it contains, such as the nature of Magical Damage, are canon and often alluded to in later seasons.
 * Death Note has a tie in novel in the form of Death Note:Another Note, which tells the story that was (very briefly) mentioned about L working with Naomi Misora.

Comics

 * Batman -- In addition to the novelizations of the movies, and even the comics (The Knightfall storyline was novelized), Batman has had several stand alone novels like The Ultimate Evil.
 * Superman -- Has had tie-in novels since the 40s.
 * Spider-Man -- Had a rash of novels in the 90s by Diane Duane. More recently Jim Butcher has been writing them as well.

Film

 * The Sixth Sense had a novelization and a series of sequel books dealing with Cole's attempts to continue helping the living-impaired.
 * Twelve tie-in novels based on Dirty Harry films were released in the early 80's.

Live Action Television

 * Doctor Who -- At least two hundred original novels, filling the expanded branch of the Whoniverse during the 16-year hiatus in between the series' cancellation in 1989 and its dramatic uncancellation in 2005, and continuing after the series' return, first from Virgin Books (Virgin New Adventures) and later from BBC Books (Eighth Doctor Adventures). Both publishers produced ongoing adventures for the 'incumbent' Doctor of the time (the Seventh Doctor and onwards), as well as "Missing Adventures" (Virgin Missing Adventures for Virgin, Past Doctor Adventures for BBC Books) squeezed into gaps in the previous Doctors' timelines. Some of the writers ended up working on the 2005 revival television series.
 * A long series of novelisations preceded the original novels, of almost all the stories broadcast in the show's 26-year first run. They ranged in size from about 120 pages (for a two-parter) to about 400 pages (for a six-parter), which meant that a lot either got cut out, or should have been.
 * Torchwood has a number of them. The stories range from the reasonably logical to the ridiculous, and deal with every trope you can possibly thing of from zombies, to the Invisible Man routine, to card games being serious business, to Gender Bending.
 * Babylon Five -- notable for having the tie-ins be Canon, with series creator J Michael Straczynski reviewing them and/or providing outlines. Events described in the novels were more than once later referenced in the series.
 * Star Trek -- A huge range of novels based on all eras of the franchise (and the spaces in between) exists, including novelizations of several episodes and Star Trek New Frontier. Other than the novelizations, these are all officially declared non-canon by Paramount and Gene Roddenberry. When Jeri Taylor was the Word of God on Star Trek Voyager, her original novels about the crew's history were considered canon. They aren't any more.
 * Blakes Seven -- Produced a novel, "Redemption", by the series' star Paul Darrow, as well as one by Tony Attwood. There was also at least one set of episodes novelized.
 * Buffy the Vampire Slayer -- both original novels and novelizations. Novelizations typically span several episodes (the entire seventh season was novelized into a single 500-page novel).
 * Bones -- As of this writing only one exists, but it's notable because the show itself is (very loosely) based on a book series, but this new book is based entirely on the television continuity.
 * Quantum Leap has a small body of novels, including both novelizations of episodes and original novels; among the latter are a "prelude" to the series and at least one explicit follow-up to a broadcast episode (Angels Unaware by L. Elizabeth Storm, which revisits characters from the episode "Another Mother").
 * Smallville: Copious numbers of books have been released, which tend to be Mary Sue Fanfic level quality (meteor freaks more powerful than Clark, a new perfect love interest that seduces Clark and dies tragically, and so on). This is not always the author's fault -- as the Television Without Pity crew will tell you, the actual series is just as poorly written.
 * Sliders: The Novel, by Brad Linaweaver adapts the pilot episode into printed form.
 * Red Dwarf: Two novels by "Grant Naylor" -- a pseudonym for series creators Rob Grant and Doug Naylor -- as well as novels written by Rob Grant and by Doug Naylor as solo efforts. The novels parallel some key events in the series, but stand alone from the TV show, as they have their own continuity.
 * In fact, there was some difficulty in originally finding a publisher. Grant and Naylor were afraid to use BBC books, as they figured Executive Meddling would force it to become a simple Novelisation. The result is probably the finest example of a Television Tie in Novel.
 * Sea Quest DSV had a series of three novels, one of which was a novelization of the pilot. The other novels are mediocre at best.
 * Lost had a few books featuring new castaways and their lives on and off the island, as well as the book Bad Twin which was written by a character, mentioned in the show, and played a small role in the Alternate Reality Game "The Lost Experience".
 * Murder She Wrote has many tie-in novels that are credited to the main character, Jessica Fletcher.
 * Twenty Four has the 24: Declassified series, whose entries seem to take place at unspecified points before the beginning of the first season of the show and occasionally "introduce" established characters from the show (such as the third, Trojan Horse, which was, chronologically speaking, the first appearance of ). Some of the series' authors tend toward giving such established character introductions, while others tend toward introducing completely original characters (who then often die before the end of the book because hey, why not? It's not like they have any reason to survive the book).
 * Psych now has a burgeoning series of tie-in novels.
 * The X Files has a few very short books, some of which are actually based on episodes from the show (this may also be the reason for their length). The prose is nice but very simple; you may even be forgiven for thinking that they were meant for younger readers, but the subject matter isn't any less child-unfriendly than it normally is on the show. It'd be really cool if someone wrote full-length novels based on Mulder and Scully's adventures, though.
 * They did. Kevin J. Anderson wrote three of them. That should tell you enough.
 * A series of Columbo books featured the title detective investigating murders somehow connected to famous crimes of the past (though not always directly; in one, a man murders his wife and her lover and attempts to confuse the investigation by writing "Helter Skelter" and other phrases from the Manson murders on the walls in their blood).
 * Supernatural has a small series of tie-in novels, with six books already published or soon to be released. Their connectivity with each other and the series depends on the author, but most will at least mention events in the series that happened recently in relation to the novel.
 * Highlander the Series has some novels and an anthology that are considered canon. The concept behind the show of immortals Walking the Earth lends itself well to these tie-ins.
 * Alien Nation is an unusual case of tie-in novels continuing the series after its cancellation. In particular, the tie-in novel series included two novelizations of scripts that were meant to be future episodes of the series (Dark Horizon and Body and Soul), which were later made into Made-for-TV Movies.
 * Stargate SG 1 had a novelization of the pilot episode and four original tie-in novels by Ashley McConnell early on. They're mostly known for their poor editing and continuity errors, such as referring to characters by their actors' names. The current series of tie-in novels is published by Fandemonium, who originally sought out Stargate fanfic writers. The company went on to publish Stargate Atlantis and Stargate Universe novelizations and tie-ins as well.
 * There was also a series of five novels by Bill McCay based on the original Stargate movie, which take place in an entirely different continuity than the series.
 * Forever Knight had three official tie-in novels written by fanfic writers.
 * Clueless had several YA tie-ins, based on both the movie and the TV series.
 * The Castle tie-ins, rather than being books about the series, are the books that Castle is ostensibly writing in the series.
 * All three CSI series have a number of tie-in novels.
 * Merlin has a number of episode novelizations.

Professional Wrestling

 * Would you believe, Professional Wrestling, specifically WWE, has had a couple of these? One, Journey into Darkness, details the Start of Darkness of everybody's favorite giant, psychotic pyromaniac, Kane, while another, Big Apple Takedown, has the government forming a covert-ops team of WWE wrestlers.

Toys

 * Transformers: Obviously a massive amount of children's books, but recently, a number of novels for older readers have been produced as well. The Official Transformers Fanclub also semi-regularly releases official short prose stories to its members which take place in its own continuities. The answer to "What's Canon with regards to Transformers?" is "Yes". Let's not get into it.
 * Bionicle had multiple series of junior novels, some of which told new stories not based on the comics or movies. However, these were not treated as tie-ins but as full canon, dealing with the main story arcs and doing it more in-depth than the other mediums usually could. Additionally, all but the first few were written by one of the franchise's main story editors, who also wrote the comics and web serials.

Video Games

 * A video game example: the Backyard Books, based on the Backyard Sports series. They are more this than novelizations because the games have no plot (except for Skateboarding, but there is no book based on that game).
 * The Elder Scrolls Novels are, at the moment, a two-part novel series between the events of Oblivion and Skyrim. No word on whether or not there will eventually be more.
 * Hitman has a tie-in novel named Hitman: Enemy Within. The novel's plot is set between Hitman 2: Silent Assassin and Hitman: Blood Money and revolves around a rival murder-for-hire organization, known as Puissance Treize (French for "Power Thirteen"), attempting to destroy Agent 47's employer, the International Contract Agency (ICA).
 * King's Quest has not just an official strategy guide that also serves as novelizations of the games themselves with extra information, but also three little-known original-story novels.
 * Pokémon -- Had a couple of picture books based on various episodes: "Bye-Bye Butterfree" and "Attack of the Prehistoric Pokemon". It also had numerous tie-in manga.

Western Animation

 * Spongebob SquarePants had novelizations of its first few episodes. Very awkward novelizations, created from translating the script into prose.
 * Novelizations of episodes are available for numerous Nickelodeon shows (except The Ren and Stimpy Show  and Ka Blam) from the past fifteen years or so.
 * Star Trek the Animated Series.
 * Alan Dean Foster's Star Trek: Log books were novelizations of the episodes (much as James Blish did for the original show) expanding on the bare bones thirty minute plots. Starting with three episodes per book, he managed to create whole books out of one episode as time went on.
 * Many Trek novels referenced it even when official Trek canon did not.
 * When Doug went to Disney, a few episodes of the show were part of the Disney Chapters collection of books. About a year later, Doug got not one, but two spin-off titles: Doug Chronicles, which were original stories about the title character, and Doug Mysteries, which was the same thing but as mysteries.
 * A number of Recess episodes were also part of the Disney Chapters series in the 1990s, most notably, "The Experiment".
 * 101 Dalmatians: The Series got a tie-in novel released shortly before the show premiered, "Cruella Returns". It tied four episodes together ("You Slipped a Disc", "Leisure Lawsuit", "Cone Head", and "Snow Bounders"), with many differences from what actually happend in the episodes (such as Mooch's gang being made up of a bunch of random stray dogs instead of Dipstick and Whizzer, etc.).
 * Many animated Disney and Pixar films will inevitably have thousands of tie-in novels and stroybooks. Some of them are straight-up retellings of those movies' plots, while others are sequels to said movies. For example, The Lion King was actually accompanied by several tie-in books that not only recounted that movie's events, but also covered more information about the film's main characters, such as how Scar got his um, scar in the first place and what was his name before he even got that scar. However, some of the events that happened in those books are actually not considered canon with the movies (for example, another Lion King-based book claimed that Simba had a son, but the Direct to Video sequel had Simba bear a daughter).