Encyclopedia Exposita

"In many of the more relaxed civilizations on the Outer Eastern Rim of the Galaxy, the Hitch-Hiker's Guide has already supplanted the great Encyclopaedia Galactica as the standard repository of all knowledge and wisdom, for though it has many omissions and contains much that is apocryphal, or at least wildly inaccurate, it scores over the older, more pedestrian work in two important respects. First, it is slightly cheaper; and secondly it has the words DON'T PANIC inscribed in large friendly letters on its cover."

- The Hitchhiker's Guide to the Galaxy

Quotes from other fictional books being used as an Epigraph or part of the frame of the story. They are not part of the text proper.

These quotes are always apposite, and often provide painless Exposition, rather than relying on As You Know -- style conversations. In Speculative Fiction, fictitious encylopedias are often used, such as Asimov's Encyclopedia Galactica. Journal entries or biographies can also be used. Can be part of a Scrapbook Story. In Video Games these tend to be more-or-less random and not immediately relevant to the story and can be used give the player something to read on a Loading Screen.

Comic Books

 * The tracts of text ending each issue of Watchmen are usually presented as excerpts from books, reports, etc.
 * "Old jungle sayings" in the classic newspaper comic The Phantom.
 * A quote from The Herodotus Complex by P'oilgof Livy starts every Buck Godot Zap Gun for Hire trade paperback, as well as each issue of the story arc "The Gallimaufry."
 * Relevant excerpts from Fleeztrow's Guide to the Gallimaufry are also part of "The Gallimaufry."

Fan Fiction

 * At the start of each chapter of Kyon: Big Damn Hero there are extracts of self-help books on being a hero, some poetry, or texts that are implied to be from future documents/books, usually relevant to the chapter.
 * Tiberium Wars likes to begin each chapter with a quote from one of the characters involved, and often ends with a hefty excerpt from military intelligence reports or research papers, making it clear that the author's done his work and knows his way around the Tiberium 'verse.
 * By the same author, Renegade features Codex entries in line with those from Mass Effect, to better explain how the addition of Tiberium to the setting has made things very different.

Film

 * In the film 2012, Jackson Curtis's unsuccessful sci-fi novel Farewell Atlantis is symbolically important and is brought up throughout the film. Parts of it are read aloud on two or three occasions.

Literature

 * The Encyclopedia Galactica, Isaac Asimov's Foundation series.
 * The Book of Counted Sorrows, Dean Koontz, repeatedly.
 * The Book of Counted Joys, Dean Koontz, not quite as often.
 * The Secret Book of Cadwallon the Druid, Deverry.
 * Princess Irulan's histories in Dune. All of Frank Herbert's Dune novels make use of this, quoting from fictional (auto)biographies, treatises on religion/politics, journals...
 * Not to mention almost every other major work by Herbert.
 * The Guide itself, The Hitchhiker's Guide to the Galaxy
 * And sometimes the Encyclopaedia Galactica in the series, although the Guide has the major selling point of being slightly cheaper and having "Don't Panic" printed in large friendly letters on the cover. As well as not taking up a parking lot.
 * Also subverted; sometimes the Guide's entries were full of non-sequiturs and gags completely irrelevant to the story. Sometimes these were never mentioned again, and sometimes they became plot-critical brick jokes as a double-subversion.
 * The biography of Thursday Next, and several other fictional documents, in the Thursday Next series.
 * The introduction to Michael Crichton's The Andromeda Strain is written as an introduction to some official report of the events of the novel. All his novels after that one followed suit.
 * Juliet McKenna likes them even more; she prefaces nearly every chapter with a fictional document, some of them only tangentially relevant.
 * The Encyclopedia of Marvels, Life Forms and Other Phenomena of Zamonia and its Environs in The Thirteen and A Half Lives of Captain Bluebear.
 * The protaganists Rules and Things to having a Funner Life in Bud Not Buddy.
 * The title and chapter pages of Stephen King's more epic novels quote anything and everything from T.S. Eliot and Thomas Wolfe to Blue Oyster Cult and King's own fictional characters.
 * The Farseer and Tawny Man trilogies by Robin Hobb.
 * The Myth Adventures humorous fantasy novels written by Robert Lynn Asprin. Each chapter has a fictitious quote. An example might be something like, "Violence is never the right thing to do" - Attila the Hun.
 * Asprin has commented that he bitterly came to regret doing this, as making up all the quotes proved to be the hardest part of writing the novels. The later books in the series drop the practice.
 * Jack McKinney's Robotech Tie In Novels used quotes from various in-universe sources to comment on the events of each chapter.
 * The Tough Guide to Fantasyland by Diana Wynne Jones calls these "gnomic utterances". One of her novels, Fire and Hemlock, also uses quotes from the ballads "Tam Lin" and "Thomas the Rhymer" in this way.
 * The prologue of So You Want To Be A Wizard quotes extensively from the wizard's manual in order establish what wizards are and how wizardry works.
 * The Young Wizards series in general contains a few quotes from the Book of Night with Moon.
 * American Gods has quotations from a book being written by one of the characters, Mr Ibis.
 * Jonathan Strange and Mr. Norrell did this frequently; the characters often debated the relative merits of the books.
 * Pournelle's CoDominium series, uses this trope. In Falkenberg's Legion, it was used sparingly, with about 3-4 entries in the work. Latter novels Go Tell the Spartans and Prince of Sparta have a excerpt from a number of sources, including essays, news reports, even letters, in the beginning of each chapter. In The Mote in God's Eye, excerpts appear when characters decide to look them up on their PD As, and flow smoothly with the narration.
 * Oddly enough, the sequel to The Mote in God's Eye actually (for the most part) uses real historical quotes.
 * Pournelle's collaborator, Larry Niven, is also very fond of this. His book Destiny's Road is full of quotes from planetary science surveys, local lore regarding the colonization of an alien world and the ultimate fate of some colonists, and quotes regarding local customs. A very early chapter opens rather ominously quoting an excerpt of a military absentee court-martial.
 * Many of the chapters in the Prince of Nothing series open with quotes from Achamian's history of the Holy War that is the focus of the series.
 * These provide at least one second-reading shudder, as a poetic epithet used in an epitaph in book 1 is given graphic and disturbing illustration in book 2.
 * The Wheel of Time
 * Animorphs does this in a couple of books.
 * Redwall
 * House of Leaves. Either half of it, or all of it, or if you're really brave, none of it.
 * Robert Rankin has The Suburban Book of the Dead, the rewritten Suburban Book of the Dead, works by the guru's guru Hugo Rune, and works about Hugo Rune by Sir John Rimmer. And that's just for starters.
 * Terry Pratchett's Nomes Trilogy features epigraphs from The Book of Nome (a Cargo Cult religious text) in the first two books and A Scientific Encyclopedia For The Enquiring Young Nome (which misunderstands things almost as much, but in a different way) in the third.
 * A Hat Full of Sky starts with an excerpt from Fairies and How to Avoid Them. It also contains part of a text on capturing hivers, although that stops when the writer goes crazy and, it's implied, gets more or less vaporized.
 * Cantra yos'Phelium's logbook in the Liaden series.
 * Each of David Eddings' books opens with a short piece of narrative taken from historical records, history books, or religious doctrines within the context of the story. These serve to establish the setting and bring the reader up to speed, sometimes serving as a roundabout recap or providing context for the events. For instance, the first book of The Tamuli starts with a record from the Tamuli government summarizing the events in the previous series; the fictive author shows a great deal of secularism by dismissing cases of divine or supernatural influence as superstitious exaggeration, and derisively criticizes unfamiliar government practices such as voting or female rulers. The second recaps more events but is explicitly written by a different author while part of the same record and calls into question the previous chapter's take on things.
 * The Trickster's Choice and Trickster's Queen have quotes of useful bits of advice Aly got at the start of each chapter - stuff from books, people she knows, etc. One example I can think of is Daine telling her that the Gods can sense lies, but if you don't make them suspicious enough to read your mind, they won't know if you left out stuff.
 * The War Against the Chtorr. "A Season for Slaughter" heads each chapter with extensive quotes from the "Red Book", a guide to the alien invaders to which the protagonist has contributed heavily.
 * Baron Bodissey's Life in Jack Vance's Gaean Reach novels - it's a twelve volume long philosophical encyclopedia which Vance often quotes, at length, for use as chapter headings. The entries aren't always entirely relevant, but this being Vance, they're always delightful. In The Demon Princes, there is also the criminal psychology manual The Demon Princes by Caril Carphen.
 * Bodissey's omnipresence is later lampshaded; a character guesses that the latest Ice Cream Koan is from Bodissey, since he's said practically everything.
 * Also quoted in The Demon Princes are several reviewers who make very hostile comments about the Baron. One expresses the desire to give Baron Bodissey a severe thrashing -- and then buy him a drink.
 * Pudd'nhead Wilson's Calendar from Mark Twain's Pudd'nhead Wilson.
 * The Empire of Man series follows in Eddings' footsteps by having the book open with commentary from a biographer who is writing from a much later point after the events in the books. Some of the things the biographer says are quite important, especially the bits that show that.
 * Cats Cradle has excerpts from the Books of Bokonon to explain Bokononist philosophy.
 * Every chapter of books in the Star Wars: Republic Commando series is preceded by an excerpt from an in-universe document. One book even had a Mandalorian-to-English dictionary as an appendix.
 * The novel-length Ciaphas Cain stories contain "excerpts" from various fictional sources - often Jenit Sulla's unreadable biography - in between chapters.
 * Robert E. Howard puts epigraphs of dramatically manly poetry before each chapter of The Phoenix On The Sword, but does not do this for other Conan stories.
 * Charles Sheffield's Summertide (book 1 of the Heritage Universe) has excerpts from Lang's Catalogue of Builder Artifacts to explain the mysterious structures mentioned throughout the book. Extra points to the fact that the author of the catalogue is a main character.
 * The Grimnoir Chronicles uses quotes from a variety of sources at the beginning of each chapter. Some are from or about characters in the books, but many just fill in details of the world, such as Theodore Roosevelt dying in combat against the Kaiser's zombies in World War One.
 * Played with in Keith Laumer's Retief series. Many of the stories start with an excerpt from the official records of the CDT, explaining the story you're about to read. The official version never comes close to describing what actually happened, and Retief is rarely mentioned, let alone given credit for saving the day.
 * Some Doctor Who Expanded Universe novels have these. Theatre of War had excerpts from its fictional playwright's work, and scholarly works about his plays and theatre in general. The Also People quoted fictional pop songs, including regular DWEU unseen background character Johnny Chess, Silurian punk ("Outta My Way, Monkeyboy" by Third Eye), and Cyberman blues ("Tears of Rust" by Cyberblind).

Television

 * Gene Roddenberry´s Andromeda.

Tabletop Games

 * Sarpadian Empires, which provides much of the flavor text to the "Fallen Empires" expansion of Magic: The Gathering. Much of Magic's flavor text counts as this, actually, but this is the most iconic example. Sarpadian Empires, Vol. VII appears as an actual card in the Time Spiral set.
 * Many Kamigawa block cards quoted extensively from fictional sources, as flavorwise the texts represent a retrospective historical view of the Kami War. The most common source to be quoted from is The History of Kamigawa, including a card of the original author tome.
 * Too many to count in the margins of Nobilis, most notably the works of Emily Chen (Doorknobs, Viridian, A Small Detour To Altair and others), Kneader Guy (Earth Stories, Air Stories, Fire Stories and Water Stories), Luc Ginnes (On Serving the Nobilis, Legends of the Nobilis and Void Stories), Jackie Robinson (Parables for Our Modern Age and Small Gods), Merriweather James (Principals of The Dark), and Agusta Valentina (A Philosophy of Treason). So extensive was the collection of works with "excerpts" in the book that many readers were surprised to learn that none of them were real.
 * A variation appears in many Shadowrun sourcebooks, where a running discussion of the main text, in electronic discussion forum format and complete with the occasional off-topic digression, will appear in the margins or along the bottoms of a book's pages.
 * White Wolf loves these, especially in both versions of The World Of Darkness.
 * Paranoia: XP Service Pack 1 has numerous examples. Early in the book, one of the pages is duplicated with text messages from hackers covering it, and the first letter of every sentence supposedly spelling out a secret message: "MIKE-U LIVES".
 * The next page repeats the trick: "NO HE DOESN'T".
 * The 2nd edition rulebook presents "Tips for Traitors" as an excerpt from a much larger in-universe document.
 * Reading the above is considered metagaming. Metagaming is treason. Please report immediately to your nearest Termination Booth.
 * The Van Richten's Guide series of Ravenloft supplements use this device constantly, both as in-character 'citations' by in-character "author" Van Richten, and as flavor-text sidebars. Such references come from personal journals, ship's logs, letters, and other written testimony from individuals who have encountered dangerous monsters; hence, the Undead Author trope often comes into play. Sometimes literally.
 * Warhammer 40000's Codices and rulebooks are littered with character quotes or extracts from top-secret Inquisitorial reports, to provide an extra bit of background and flavor while giving certain elements of the fanbase something to argue about.

Theatre

 * In the musical How to Succeed In Business Without Really Trying, the protagonist repeatedly turns to an advice book of the same name.
 * Which actually exists: Shepherd Mead wrote a series of cartoon books in the 1950s which were parodies of then-current how-to books, one of which provided the title and inspiration for the musical. The book was republished in 1995 with the revival of the musical.

Video Games

 * The Codex in Mass Effect
 * A bit subverted, since the Codex is sometimes wrong: It's an in-universe document and therefore limited to what is public knowledge, not what the player finds out.
 * And the Codex is also occasionally made deliberately wrong by its in universe makers; one shining example is in ME 2 when you look up 'Sovereign.' Apparently, Mr. Vanguard-of-Our-Destruction was a geth ship that just happened to look like a Reaper. Uh-huh.
 * In the Expanded Universe novel Ascension, the character Gillian Grayson starts reciting a page from a textbook. The words are taken word-for-word from the Codex.
 * Played in Sid Meier's Alpha Centauri and Civilization IV, where every single technological advance, facility and secret project is accompanied by a quote from either a real book, or in the case of the former, a book, interview, memo, or famous work, real or fictional.
 * In the Designer's Notes of Alpha Centauri, Brian Reynolds said that Frank Herbert was his favorite science fiction author and cited The Jesus Incident as "the most important influence on the story of Planet".
 * The Pokédex, which is devoted to providing information about Pokémon, such as appearance, attributes, and locations. Though, it's vague whether or not the entries read in-game are meant to be excerpts or the full thing. Also, some of the entries are likely made on the spot by the device in-universe, such as with Legendaries, whose abilities were not exactly common knowledge among Poké-experts except as folklore.
 * The Logbook scans in the Metroid Prime series.
 * When the player accesses the mission objectives screen in the Aliens vs. Predator 2 game, they are also presented with short excerpts from the "incident report" compiled by Weyland-Yutani after the end of the game. It is both used as an atmospheric framing device, and a way of including subtle Foreshadowing - for example, in the mission where the Predator first appears, the report excerpt categorically states that despite the insistence of certain parties, there was no physical evidence of the involvement of a third species. Also, each level in the game begins with a timestamp, such as "Incident minus two days," "Incident plus three weeks," or the ominous "Incident Start."
 * Many of Infocom's Zork computer games featured the Encyclopedia Frobozzica.
 * Each "act" of Tech Infantry has an epigraph quote either from a real or in-universe fictional work of literature, poem, song lyric, or a pithy quote from an in-universe fictional character. The title of each "episode" (four acts) is taken from the epigraph to the last act of that episode. Which means the episode title, and by extension the fourth-act epigraph, is chosen before anything beyond act one of that episode is written.
 * Historical quotes in Call of Duty.
 * Imperial slogans on the main menu of the Dawn of War games.
 * The quotations on the death screen in Operation Flashpoint, such as "War is not nice - Barbara Bush".
 * A not quite known puzzle-strategy (yeah) Netstorm had an extensive manual with in-universe quotes used as epigraphs.
 * "Avoid taking drugs, it ruins you." from Little Fighter 2.
 * The information screens in Age of Mythology were full of these.
 * The loading screens of the later Total War games (Rome and Medieval II) have these. Plus in Shogun there's a philosipher in the throne room, who if clicked on gives you random quotes from The Art of War
 * Bioshock has quotations by its own characters during loading screens.
 * Nearly all of which you can find a recording of in their original context at some point in the game.
 * Star Ocean Till the End of Time and Star Ocean the Last Hope feature an in-game Dictionary, which is updated with new entries as the story progresses and terms are brought to light. They are even categorized by topic, such as "Planets", "Technology", "Species", and so forth.
 * Final Fantasy XII has an expansive bestiary which hold theories and information about the various monsters, people and Espers the party defeat in their travels. In addition, killing enough of the specific types of wild encounter uncovers additional information about the places in Ivalice, and sometimes about rare items that certain enemies randomly drop.
 * Vagrant Story opens with a quote from famed historian Alazlam Durai, author of The Durai Papers: 400 Years of Truth.
 * Final Fantasy XIII took this a step further - the datalog mixes entries like this in with All There in the Manual.
 * The Compilation of Final Fantasy VII has the play Loveless which is incredibly popular in-game. Crisis Core references it most often though it makes less sense than it had in the original game.
 * The Church Of The New Epoch's mission briefings in Syndicate Wars include quotes from their religious text.
 * In Famous: the major story divisions through the game come with quotations from various historical figures.
 * Several characters in Final Fantasy IX are theater buffs. One particular fictional play, I Want To Be Your Canary, has particular symbolic importance to the plot, and a few characters quote it during plot sequences.
 * The whole Warcraft oeuvre, especially the trading card game, uses fictional quotes from various plot-important characters to tie the whole expanded universe together.
 * Both playable races in O.R.B: Off-World Resource Base consider an ancient document called the Torumin their Bible, some parts of which are quotes in the game.
 * In Dragon Age: Origins, the player occasionally finds parchments with fictional poems, stories, and legends throughout Thedas. These are logged into the game's Encyclopedia Exposita along with game-relevant information.
 * Snatcher does this with a supercomputer that contains a lot of information about the game world.
 * In Deus Ex, there are several books and newspapers that the player can read.
 * In Valkyria Chronicles, the entire game is setup like a history book that is divided with tabs that contain the main story and recorded entries about characters and weapons.

Web Comics

 * Hardwick and Little's Bestiary, Gunnerkrigg Court, Chapter 3.

Web Original

 * In the Whateley Universe, the author of the Phase novels often does this, with quotes from rock songs as lead-ins for chapters. But the quotes are usually from the fictional band Brass Monkey, so they can be as relevant as the author wants.
 * Used in Look to the West, which generally has the structure of an initial quote which may or may not be relevant to the rest of each chapter, and then the main text also supposedly extracted from in-timeline books. Occasionally inverted with the starting quote being taken from our own world's history.
 * In Guild Of The Cowry Catchers, the quotes beginning each episode are from a pair of books by the Hero Antagonist and leader of the titular La Résistance.
 * Go type about:mozilla in the URL box in any Mozilla browser from Netscape Navigator 1 all the way up to the current version of Firefox. (Original Web? Not exactly, but close enough.) Or just google "Book of Mozilla".
 * Each chapter of the various campaign archives from The Global Guardians PBEM Universe began with quotations from some in-universe source. While most of these were off-hand (yet relevant) comments from the characters involved about the action presented in the chapter, sometimes they were quotations from such items as An Examination of Irregular Wave Forms and Power Phasing Effects in the Jaffe Battery (better known as the "Ray Gun Paper"), Genetic Inflexibility and Geographic Isolation as Influences in Metagene Frequency (a scientific study on why certain regions of the world have more superhumans than others), and The Book of Holy Power. the religious scripture of the Church of Jesus Christ, Superhuman (a cult that teaches that Jesus was a Metahuman who will one day return from his "sojourn" with an advanced alien society somewhere in space).