Divided for Publication

You've written a long book. Lots of characters, many Plot Threads, and deep, complex Character Development. Your publisher likes it, but unfortunately, you're not a very well-known writer, and readers aren't likely to pick up such a vast novel. Furthermore, limitations in the current printing and binding market make publication as a single volume uneconomical, especially if this is a debut novel; if it goes over 424 pages in length, it must be outsourced to a bindery that uses a more expensive technique, disproportionately increasing printing expenses.

The solution? Split the book into multiple volumes. The public will be less intimidated by the shorter length of the individual volumes, and thus more likely to buy them. There are also some practical reasons. For one, the smaller books are individually easier to hold and carry. Two, it places less physical stress on the bindings, so smaller books are less prone to fall apart while the consumer is still reading them. Three, it's easier to sell a cheap book than a costly one. There are also some economic issues in that the large page count has a higher per-volume production and transport cost, so it makes sense to divide that out to maintain a reasonable profit margin and/or price point.

If the book proves successful, it will probably be later released in a single-volume edition.

This happens with translated works, pithy phrases in the original language often require more words. In particular, English books translated into Romance languages get much wordier.

Note that this trope isn't intended for a series of books that tell a single story. This trope is for those stories submitted as single books, that were then split into multiples at the publisher's request.

A forerunner is the Victorian three-volume novel, a longer story is told and sold in three parts. In the 19th century, the business model was to use the first volume to get people interested in the second and third parts, and thus extract more money per story.

See also Trilogy Creep, One Game for The Price of Two, Multi Volume Work.

Film

 * In the Name of The King, the Dungeon Siege adaptation by Uwe Boll, narrowly averted this. The original cut was over 200 minutes long and was planned to be split into two movies for theatrical release, but the editors couldn't find a spot in the middle where there was a good place to end the first installment. Instead, it was released as a single, heavily-cut two hour film in theaters and on DVD. The Blu-ray had an "Unrated Director's Cut" that restored a half hour of cut footage.
 * The movie Che about the life of Guerilla leader Ernesto 'Che' Guevara had to be divided into two parts.
 * Kill Bill was originally going to be one movie, but was split into two volumes for release.
 * The film adaptation of Harry Potter and The Deathly Hallows was split into two parts, as the plot is very dense and the filmmakers decided that splitting it into two movies is a better choice than compressing the story.
 * Before production of Harry Potter and the Goblet of Fire, the producers considered splitting it into two movies, but decided against it. Consequentially, a few subplots had to be cut out for time.
 * Predictably, cynical film critics everywhere assumed there was a less noble motivation behind the decision.
 * Breaking Dawn seems to have taken a page out of Harry Potter's book and is split into two parts. As little of significance happens in the story, this was a purely money-grubbing decision.
 * Richard Lester's The Three Musketeers 1973 and The Four Musketeers were originally made as one film. It was only in post production that they decided to break it up into two parts. Many of the actors involved were somewhat upset, since they were only paid for one movie.
 * The Salkind Superman and Superman II were originally conceived as one film.

Literature

 * The Lord of the Rings was famously split into three volumes for publication, and in fact to this day is commonly (and erroneously) referred to as a trilogy. It is technically a single novel.
 * This is further confused by the fact that each of the three "parts" -- The Fellowship of the Ring, The Two Towers, and The Return of the King -- is divided into two of what Tolkien called "books", making six "books" in total. This is using the meaning of "book" as a division of an epic.
 * Similarly, the Illuminatus! trilogy was originally pitched as one book, but split into three to have some hope of actually being read.
 * Elizabeth Moon's The Deed of Paksenarrion also had to be split into three volumes.
 * David Weber's first Hells Gate novel was split into two books, and it seems likely the same will have to happen to his next Honorverse novel, A Rising Thunder.
 * Charlie Stross's first The Merchant Princes novel was split into two books.
 * Succession was split into two volumes, The Risen Empire and Killing of Worlds. Confusingly, the book was published as a single volume in the UK, under the title The Risen Empire.
 * The UK edition of A Storm Of Swords was split into two volumes, Steel and Snow and Blood and Gold. The French edition split it into four volumes - and, in fact, the French translations of all the A Song of Ice and Fire books were split into at least two volumes.
 * The first two books from The Wheel of Time were split in half as part of a 'young adult special edition'. This doesn't seem to have done well, none of the other books were split. The German translation of the series has passed 31 books, corresponding to the first 11 books and prequel in the English version.
 * The final book - A Memory Of Light was originally intended to be one book- it has been announced that it will be split into three.
 * The Nights Dawn Trilogy was split into six books for the American release.
 * Clive Barker's Imajica was split into two volumes.
 * The Tale of Genji, due to its sheer length, is frequently divided into two volumes.
 * The Finnish translation of the Memory Sorrowand Thorn trilogy was split into no less than twelve volumes. Even in English, the final volume was split in two for the paperback editions.
 * From the same author, Otherland has at the beginning of the first book an admission that it wouldn't be a series if it weren't for the fact that the author needs to keep writing new books at a constant pace so he'll keep receiving royalties.
 * Tad Williams is very good at this. There's a note at the front of Shadowrise remarking that the quartet was originally meant as a trilogy, and "one of these days I will learn to write a last volume that doesn't need its own zip code."
 * CJ Cherryh:
 * In the Chanur series, where the middle three of the five novels were one novel split into three to satisfy publishing constraints; they form one story arc, with no mini-resolution at the end of each. Although they've been published together in an omnibus since, but have never been printed as Cherryh really intended, as one novel.
 * Also, Cyteen was published in mass-market paperback form as three novels, although it was released in hardback and "trade paperback" form as a single work.
 * Proust's In Search Of Lost Time was originally published in seven volumes, due to its length. Modern versions are usually in 2, 6 or 7-volume sets.
 * Lois McMaster Bujold originally submitted the first two books of The Sharing Knife as a single book.
 * Inverted with Jonathan Strange & Mr Norrell, which was intended to be in the style of the Victorian three-volume novel, but ended up as one giant-ass book.
 * In a weird case, The Belgariad was originally intended to be a trilogy, with the three volumes named Garion, Ce'Nedra, and Torak after three key characters in the story. The author was asked to split the story into five parts instead of three, resulting in the series as we know it. This is noticeable starting in the second book:
 * The climax of the second section (of three) in the second book is the climax of the main character's development up to that point.
 * The final section of the second book is a mostly self-contained episode in the story, but it sets up the quest that takes all of the third book (which ends on a Cliff Hanger) and that isn't properly resolved until early in the fourth.
 * The second half of the fourth book and all of the fifth book function together as a single unit, with most of the main character's subplot in the fourth book and almost all of the Supporting Leader's subplot in the fifth book.
 * The Dutch translation of the later "stand alone" books of The Belgariad (Belgarath the Sorceror and Polgara the Sorceress) and of The Redemption of Althalus were all published as two books.
 * Same for the French translation of the former.
 * Clive Barker's Books of Blood.
 * The King Killer Chronicles: Rothfuss wrote the whole story over 14 years, submitted it, then publisher says make it a trilogy, so he has to rewrite it yet again.
 * Romance of the Three Kingdoms is often divided for publication.
 * Ash a Secret History by Mary Gentle was split into four parts for US publication.
 * Three-volume novels? Jane Eyre comes to mind, though it's now typically published as an omnibus.
 * The second and third of Garth Nix's Old Kingdom books are basically one story, but apparently after finishing Lirael he realized that this was getting way, way too long for a single young-adult-aimed fantasy novel and split it in half.
 * The first book of The Riftwar Cycle by Raymond E. Feist, Magician, is usually published in two parts, called Magician: Apprentice and Magician: Master.
 * This may vary by region. In Australia it is more common to find it published as a single volume and only imported versions split into two parts.
 * Back in the day, this happened with some non-fiction books as well. There are dual volume versions of John Toland's The Rising Sun and William Shirer's Rise and Fall of the Third Reich, and to this day, some publishers still release Solzenitsyn's Gulag Archipelago in three volumes.
 * The German translation of Vision of the Future was split into two volumes.
 * Another translation split. The Japanese versions of the Honor Harrington books are split in two starting with the third or fourth book. Possibly more with the later volumes
 * The Bible's Old Testament books of 1 Samuel, 2 Samuel, 1 Kings, and 2 Kings were originally one book. So were 1 Chronicles, 2 Chronicles, and Ezra (the dividing line between the end of 2 Chronicles and the beginning of Ezra is in the middle of a sentence). These were split in the Septuagint, with the Vulgate following the same convention, because the scrolls used by those "publishers" couldn't fit the text of the whole book. Making this Executive Meddling that's Older Than Feudalism.
 * The second volume of the Wars of Light and Shadow series, Ships of Merior was such a Doorstopper that it couldn't be published in paperback form as one book. So the paperback version is split into two volumes, entitled Ships of Merior and Warhost of Vastmark.
 * This happened to Isaac Asimov several times, most notably with his autobiography. He hated this more than other authors, because he would then have to decide whether to count it as one item or two on his list of published books, with good arguments for either choice.
 * Not quite an example, but related: some editions of Haruki Murakami's Norwegian Wood split the novel in two very small volumes, one red and one green (sometimes inside a gold-coloured case, as per here). As the novel is not particularly long (and in at least one case the split causes a mid-chapter break), this was presumably done for strictly aesthetic reasons.
 * Harlan Ellison's anthology Again Dangerous Visions was published in two volumes in UK hardcover, but confusingly split into three volumes in paperback.
 * The first story in Alan Dean Foster's Spellsinger series was split into Spellsinger and The Hour of the Gate.
 * Sergey Lukyanenko's Seekers of the Sky was split into Cold Shores and Morning Nears with the second novel picking up immediately after the first (after a day-long Time Skip).
 * While this may also seem to be the case with his Rough Draft and Final Draft novels, as Final Draft picks up a few hours after the ending of Rough Draft, it took Lukyanenko 2 years to write the sequel.
 * This has happened twice to novels by Robin Hobb, much to many readers' confusion. The first two books of what is now known as the Rain Wilds Chronicles were written as a single book that was split into two. Hobb then set out to write a sequel which was also split, resulting in books three and four of the series.
 * Gene Wolfe's The Book of the New Sun was written as a single novel and published as a series of four. Most later editions of it divide it into two books.

Video Games

 * The text adventure game Dungeon, originally developed for the PDP-10, was adapted into the Zork trilogy for microcomputers, due to memory / disk size limitations.
 * Zork 1 and Zork 2 are the two halves of the original Dungeon, with a few details added to each to round them out. Zork 3 (other than one puzzle) was developed de novo by Infocom.
 * Sonic 3 and Knuckles. It had to be split into two cartridges: Sonic 3, and Sonic and Knuckles. However, thanks to the "lock-on" technology, which allowed users to insert their Sonic 3 cartridges onto Sonic and Knuckles, this became kind of a good thing, as otherwise Knuckles probably wouldn't have become playable, much less in Sonic the Hedgehog 2
 * Golden Sun and its direct sequel were conceptualized as one game. When the game shifted from the N64 to the GBA, it had to be split due to space limits. However, one could argue that the narrative ended up better as a result:
 * In Japan, the PC Engine port of R-Type was released in two separately-published HuCards titled R-Type I and R-Type II. R-Type I contains the first four stages and after completing them, the player is given a password that could be used in R-Type II to carry over the player's lives, score and power-ups from the first game. Likewise, finishing R-Type II gave a password that starts the second loop in R-Type I. In America, Hudson managed to combine both games into one TurboChip and the game was later re-released in Japan as R-Type Complete.
 * The first two games in the Ys series, Ys and Ys II, were designed to be played one after the other. Later remakes, starting with the TurboGrafx-CD version, combined them into one complete package.
 * The Shenmue series was supposed to be released in serialized installments that would have spanned 16 chapters across at least three or four games. But since the first two games failed to recoup their expensive development budget (even after Shenmue II was ported to the Xbox), the third game in the series has languished in Development Hell since Sega almost fell into bankruptcy as a result of the series' commercial failures (forcing the company to quit the hardware race and become a third-party developer for their former competition).

Web Original

 * Ursula Vernon of Digger fame had a Web Serial Novel called "Black Dogs" which is making the jump to print in two parts - as of mid-2009, only Part One is out.