Worldbuilding

""It is necessary to create constraints, in order to invent freely. In poetry the constraint can be imposed by meter, foot, rhyme, by what has been called the "verse according to the ear."... In fiction, the surrounding world provides the constraint. This has nothing to do with realism... A completely unreal world can be constructed, in which asses fly and princesses are restored to life by a kiss; but that world, purely possible and unrealistic, must exist according to structures defined at the outset (we have to know whether it is a world where a princess can be restored to life only by the kiss of a prince, or also by that of a witch, and whether the princess's kiss transforms only frogs into princes or also, for example, armadillos).""

- Umberto Eco, postscript to The Name of the Rose.

Worldbuilding is the process of constructing a fictional universe. Strictly speaking, anything that happens in that universe "builds" it, so "worldbuilding" is only used to describe the invention of fictional details for some reason other than the convenience of a currently ongoing story.

A common form of worldbuilding is the creation of history. This could just be a Framing Device for a story told by a historian, but fantasy worlds regularly include historical notes for centuries of warfare and intrigue. Stories can then be written at various points along that timeline, and each of those stories will have a clear relationship to all the others. It makes the writing of serial fiction much easier, especially if the series has multiple authors. If so, the fictional universe is a Shared Universe.

The result may sometimes be called a Constructed World, conworld or sub-creation. The term world-building was popularized at science fiction writer's workshops during the 1970s. It connotes a focus on detail and consistency. Many post-The Lord of the Rings fantasy and post-Dune Science Fiction writers use world-building in an attempt to give their stories weight and meaning that they would not have without a well-defined setting.

Constructed worlds frequently have their own aesthetics, above and beyond the aesthetics of the stories taking place in those worlds. Some artists and hobbyists build fictional worlds with no intention of writing any stories in them--at least, none more detailed than historical documents.

Worldbuilding has two separate meanings:
 * The creation of a Fantasy World Map, history, geography, ecology, mythology, several different cultures in detail, and usually a set of "ground rules", metaphysical or otherwise. Sometimes, such worlds will have a Creation Myth that's either hinted at or told in more detailed fashion. This kind of worldbuilding can go to the extreme of working out entire constructed languages. Authors typically revise constructed worlds to complete a single work in a series.
 * The work that goes into deciding the details of a setting. It's very difficult to write a story that contains absolutely no imaginary elements beyond what's described to the reader, so nearly every author worldbuilds a little bit.

In fact, the degree of worldbuilding ranges all over the scale. Extra world building that is only referred to obliquely is a Cryptic Background Reference.

See also Adventure-Friendly World, a common constraint on Worldbuilding.

TV Tropes has a World Creation Project.

Anime and Manga

 * The Alternate Universe of Wings of Honneamise Royal Space Force.
 * Masashi Kishimoto's Naruto
 * Eiichiro Oda's One Piece

Card Games

 * Over the years, this has explicitly become the goal of the creative team for Magic: The Gathering. Instead of being used to tell the story, each expansion block is now used to flesh out a different world to a remarkable degree.

Fan Works

 * The world of C'hou in With Strings Attached, a completely original world (which is a MAJOR rarity in Fan Fiction), fully realized, with two vastly different cultures and mindsets, several sets of slang, and hints of a much more ordered past.
 * And to a lesser extent, the Hunter's world, which the four visit in the Third Movement.

Movies

 * Star Wars creates quite a few worlds.

Literature

 * Shannon Hale's novels all are very lovingly crafted, this often results in a slow beginning, however.
 * William Morris' The Wood Beyond the Worlds, a major influence on Tolkien's own worldbuilding.
 * M.A.R. Barker's Tékumel created in much the same reason Tolkien created Middle-Earth.
 * Frank Herbert's Dune series.
 * Robert Jordan's The Wheel of Time, perhaps the most famous (and complete) constructed worlds in recent works of literature.
 * Mercedes Lackey's Heralds of Valdemar
 * Ursula K. Le Guin's Earthsea. Word of God says that, at least when working on the trilogy, she literally made up background information as she went along, depending on what felt right.
 * CS Lewis's Narnia
 * George R. R. Martin's A Song of Ice and Fire.
 * Also, the Thousand Worlds of his Science Fiction short stories.
 * The Saga of Recluce by L. E. Modesitt, Jr.
 * The Known Space and The Magic Goes Away settings of Larry Niven.
 * The CoDominium.
 * All of Brandon Sanderson's works, in fact, they actually all share a cosmology except for his young adult Alcatraz books, and of course the Wheel of Time books he's written in Posthumous Collaboration with Robert Jordan, Word of God says there's even a defined logic that underlies all the different magic systems of all Sanderson's works.
 * The Instrumentality of Mankind cycle of Cordwainer Smith.
 * JRR Tolkien's Middle-Earth - The original, at least in the modern sense of the detail involved. Tolkien stated that the creation of Middle-earth was the result of giving his created languages a place to live in. He has written a lots of notes on the direction of that the history of Middle-Earth should go. Much of his notes have been organized and published as The History of Middle-Earth.
 * Tolkien's world turned out so popular that nearly all Western (and some Eastern) fantasy took after him.
 * Austin Tappan Wright's Islandia
 * Jorge Luis Borges's "Tlon Uqbar Orbis Tertius" is something of a meta-example, being a fantasy about world-builders.
 * L. Frank Baum's Land of Oz is perhaps one of the earliest attempts at world building. Maps by Baum depict Oz's four regions and its neighboring kingdoms. The worldbuilding came about because of fans clamoring for more stories and places to explore. (Continuity Snarl ensued)
 * R. Scott Bakker's Eärwa (though not the entire planet), of the Second Apocalypse series, has four thousand years of human history, three huge religions, several different species, and his very own magic. Also, a completely incomprehensible Eldritch Abomination Big Bad.
 * Harry Potter indulges in quite a lot of this, the world growing more detailed and complex as the books go on, though for the most part it's Like Reality Unless Noted.
 * Robert E Howard's sword and sorcery universe, which encompasses both the Hyborian Age of Conan and the age of Kull's Atlantis.
 * Michael Moorcock's multiverse, encompassing the worlds of Elric, Corum, and various other heroes who take on the role of the Eternal Champion.
 * Garth Nix's The Old Kingdom books have a rich background.
 * Mary Hoffman's Stravaganza books are set in an Alternate Universe and Alternate History version of Renaissance Italy.
 * David Weber's Honor Harrington started off less built, but after 17 doorstoppers plus 5 short story collections with several of the short stories designed to fill the history and technology roles have built up a fairly consistent world whose technology is plausible and has rather large and detailed conflicts.
 * Safehold exploits David Weber being a more experienced author, and has very large global conflict with dozens of different political groups involved in a religious conflict. The list of characters for David Weber series is comparable with that George RR Martin.
 * Terry Pratchett has written 38 novels along with several background information books for his Discworld series, with several recurring characters and places.
 * The Vorkosigan Saga, most notably in it's description of Barrayaran history and culture.
 * Andrey Livadny's The History of the Galaxy is a vast 'verse with over 30 novels, novellas, and short stories (and counting). The order of writing does not always match up with the universe timeline (although, currently, he seems to be primarily adding to the end). Most novels have unique characters, although there are story arcs that include several of the books. There's a reason the series includes the word "history", especially since many novels deal with alien races, most of which predate humanity by millions of years and some have stopped counting at billions. One novel even goes into the origin of life itself, and another off-handedly reveals that "true" origin of Christianity. Several fan-based web MMORPGs have been created based in the 'verse, especially set during the First Galactic War, a 30-year period of constant "technogenic" warfare between two human powers, a period so devastating that its effects are still felt 1000 years later.

Live Action TV

 * Firefly has not only a map of the solar system the show takes place in as a buyable poster, but the Tabletop RPG gives us much worldbuilding.
 * J. Michael Stracynzki's Babylon 5, which has a setting with five major galactic powers and several smaller governments.
 * The Twelve Colonies of Battlestar Galactica, which were fully fleshed out by the writers for the start of Caprica.
 * Star Trek, notably in Deep Space Nine.

Tabletop Games

 * Worldbooks, a type of Sourcebook, are tabletop RPG supplements that exist entirely to give Game Masters detailed settings to run their games in. While it's possible to buy worldbooks based on the real world--essentially, history books targeted at roleplayers--most worldbooks are about fictional worlds, and so the process of writing the book consisted entirely of worldbuilding.
 * Many Dungeon Masters create their own fantasy worlds for their campaigns. Some of the more famous examples of these worlds are Eberron by Keith Baker and Forgotten Realms by Ed Greenwood.
 * There's an offshoot of roleplaying games developing that might be called "world-building games", in which the players collaborate to tell the history of a world that develops in-play.
 * Warhammer 40000 has an extremely well crafted setting with a complex history going back tens of thousands of years.
 * Warhammer Fantasy Battle doesn't have such an extensive time period to work with, but a higher number of factions and being limited to one planet means a lot more attention to small details.
 * Traveller deserves special mention as one of the best sci fi verses ever built.

Toys

 * The Bionicle universe, to the point where it has in-universe mythology and creation myths (which most members of the audience accepted in the first few years as canonical events in the timeline) that are later Deconstructed as science-based explanations for the seemingly mystical occurrences are gradually revealed.

Video Games

 * The World of The Battle for Wesnoth qualifies although it is unique as it is a open source project.
 * Akira Tsuchiya's Ar tonelico world. To summarize, he created an extensive fictional musical language as a foundation for his world, complete with a physics section on how the language works in the world.
 * Ivalice Alliance and Compilation of Final Fantasy VII.
 * The Dragon Quest games are meant to be broken up into trilogies (1-3, 4-6, and 7-9.) However, there each trilogy bar the first only has a tenuous connection with the games they frame.
 * The Warcraft series has grown from a fairly standard setting to this, including lore elements dating back ten thousand years or more. It has four worlds (Azeroth, Draenor, and to a lesser extent, Argus and Xoroth) which are explored in depth.
 * Blizzard's other big settings, Sanctuary and the Koprulu Sector, which are both getting pretty extensive supplements.
 * Metal Gear Solid
 * Mitsumete Knight thrives on this, having a rich world and mythos described in-game and in Word of God notes, and this is one of the main aspects (along with the Anyone Can Die factor) that makes it stand out in the crowd of Dating Sims. Yep, you read that right, a Dating Sim which has rich and deep World Building.
 * Dwarf Fortress is something of a meta-example, as it does this the first time you play, and can be done as many times as desired. While the set of creatures, plants, and sentient races are well-defined in the game files, the mythology, history between the races, geography, and geology are procedurally generated, according to modifiable parameters. This is a huge part of the game's charm.
 * BioWare's original properties (well, as original as a BioWare property gets) tend to be quite extensively worldbuilt. Jade Empire is a minor example, while in Mass Effect they went into greater detail. Much greater detail. And even ME is eclipsed by the Dragon Age franchise.
 * Brutal Legend has the Age of Metal, complete with a Fantasy World Map, Functional Magic based on Heavy Metal, and a Creation Myth reflecting the history of the genre.
 * And of course, there are some games where you can build a world, or at least greatly influence one. Sim games are an obvious example. And the Fable games, amongst others, allow you to shape the future of the world they're set in.
 * The Nasuverse often makes side-references to expand its magic system without it having any relevance for the actual story. The most prominent example would be the constant mention of dragons being the most powerful of all magical creatures, though nobody ever fights a dragon onscreen.
 * Marathon gets special credit for doing extensive world-building in a time when most FPS game stories consisted of "monsters teleport in, you kill them"
 * Halo started doing this with its extensive Expanded Universe, building an entire mythology around the series. The Anniversary re-release of the original game also has Terminals that give information expanding on the story to be told in the books, while those books to be written will be giving clues to the plot of Halo 4. Basically, it's like a plot cycle.
 * The Elder Scrolls has the Aurbis, the totality of existence, which encompasses Aetherius and Oblivion, and the Mundus (which contains Nirn, the world of mortals, and the continent of central focus, Tamriel), and a few other lesser planes of existence.
 * Solatorobo purportedly spent seven of its ten-year development cycle on world building, creating the Loads and Loads of Characters and the various looks and cultures of the Floating Continents.
 * Touhou owes its gargantuan fanbase to this trope. ZUN includes a surprising amount of information surrounding the characters, events and setting of the games, enough to fill several Universe Compendiums, but it is almost always bare-bones details, prompting the fans to create their own world building in any way they can, filling whatever gaps they see.

Web Comics

 * Several of the alternate dimensions of Pete Abrams's Sluggy Freelance.
 * Dominic Deegan has a story arc that was partly so the characters could unwind, and partly so Mookie could do some world building.
 * The current "space opera" story arc in The Inexplicable Adventures of Bob seems to be largely intended to pull the many disparate threads of the comic together into a coherent larger setting.
 * Snow By Night takes a Colonial-like setting with roughly equivalent places and starts its world-building by taking some clever divergences from real life. The Almanac shows it off the most.

Web Original

 * Terreneus in Grandmaster of Theft.
 * In each compilation book of Monster Girl Encyclopedia, large amount of background info were given about its world, covering how things were before, and how much it changed after the reign of Succubus Demon Lord. Quite impressive one for fetish works.
 * The Otherworld Project, formerly Eshraval, is a long-running online collaborative modern worldbuilding project founded in 2004, which also encourages Role Play in the context of the world (though not at the moment since it's rebuilding). It's recently undergone a reset, and is in redevelopment mode. Strong hints of Crapsack World in its current incarnation.

Western Animation

 * The world of Avatar: The Last Airbender
 * In the early seasons of The Simpsons Springfield semi-qualified, as its events were contained enough to function as a separate world, even if it was never defined as such. This was abandoned later on.
 * The Land of Ooo from Adventure Time is a mild example. Ooo is meant to be After the End, arising from the remains of human civilization as we understand it, and and there are hints towards this in almost every episode, including the opening sequence. Examples include mispronunciations of names like "Mozart" and "Groucho," and there's also a Nursery Rhyme that seems to be about mushroom clouds.
 * My Little Pony Friendship Is Magic slowly but surely embraces this trope as it progresses, whether it be key moments in the history of Equestria (it's founding, Discord's rule, Nightmare Moon), the methods used to alter and control nature (winter wrap-up, weather generation), the interactions between ponies and other creatures (or non-interaction, as is the case with dragons), and many other subtle details.
 * One thing that it is direly lacking, however, is a distinct map. Not even the execs at Studio B have penned an official version.

Other

 * It's rather easy to do this yourself, just open up a word processor document and let your imagination take off.
 * If you need help, the fine folks of The Other Wiki have an in-depth article on worldbuilding.
 * Or these excellent articles can help you out.
 * This Very Wiki has a couple of tips on how to help.
 * Of course, there's also the Write a Heroic Fantasy and Be the Next JRR Tolkien pages.
 * And P.C. Wrede has made a list of World Building Questions, compiled here.
 * Another good resource is Mark Rosenfelder's Planet Construction Kit, meant to run alongside his Language Construction Kit.
 * The setting of the forum role-play Open Blue has, over its extensive history, grown quite large.
 * Santharia is a world-building project for the world of Caelereth, which has been going since 1998. Everything from flora and fauna to cosmology is described in loving detail, and pictures added created by Dreamers themselves. The world of Caelereth is developed on the Development board, while on a separate Roleplaying board stories are told set within this world, most of them within the continent of Sarvonia. Recently an interactive game has been developed.
 * Friends of a Solar Empire, being (partly) a Sins of a Solar Empire fanfic, has very little Canon backstory for any of the Sins factions. So the author made one.