The Encyclopedia Galactica is a fictional or hypothetical encyclopedia containing all the knowledge accumulated by a galaxy-spanning civilization. The name evokes the exhaustive aspects of the real-life Encyclopædia Britannica.
Encyclopedia Galactica first appeared in Isaac Asimov's short story "Foundation" (Astounding Science Fiction, May 1942), later republished as "The Encyclopedists" in the short-story collection Foundation (1951). Asimov's Encyclopedia Galactica was a compendium of all knowledge then available in the Galactic Empire, intended to preserve that knowledge in a remote region of the galaxy in the event of a foreseen galactic catastrophe. The Encyclopedia is later revealed to be an element in an act of misdirection, with its real purpose being to concentrate a group of knowledgeable scientists on a remote, resource-poor planet, with the long-term aim of revitalizing the technologically stagnant and scientifically dormant empire. Originally published in a physical medium, it later becomes computerized and subject to continual change.
Asimov used the Encyclopedia Galactica as a literary device throughout his Foundation series, beginning many of the book sections or chapters with a short extract from the Encyclopedia discussing a key character or event in the story.
Theodore Wein considers the Encyclopedia Galactica as possibly inspired by a reference in H.G. Wells's The Shape of Things to Come (1933). The future world envisioned by Wells includes an "Encyclopaedic organization which centres upon Barcelona, with seventeen million active workers" and which is tasked with creating "the Fundamental Knowledge System which accumulates, sorts, keeps in order and renders available everything that is known". As pointed out by Wein, this Wells book was at its best-known and most influential in the late 1930s - coinciding with "the period of incubation" when the young Asimov became interested in science fiction, reading a lot of it and starting to formulate his own ideas.
Various authors have invoked the Encyclopædia Galactica in both science and science fiction. The first may have been author Frank Holby's short story "The Strange Case of the Missing Hero" in the July 1942 issue of Astounding Science Fiction which featured Sebastian Lelong, editor of the Encyclopedia. It was also a common fixture in previous incarnations of the Legion of Super-Heroes comic books, and has appeared in the Star Wars expanded universe and Superman comics set in the future. The "Encyclopedia Galactica" was also mentioned as being a collection of all the knowledge of a galactic Empire in the science fiction short story called "The Originist", which was written by American novelist Orson Scott Card in 1989, and took place in Isaac Asimov's fictional "Foundation" Universe.
In many of the more relaxed civilizations on the Outer Eastern Rim of the Galaxy, the Hitchhiker’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 second, it has the words "DON'T PANIC" inscribed in large friendly letters on its cover.
Robert A. Heinlein mentioned the Encyclopedia in chapter three of To Sail Beyond the Sunset (1987): "... the computer that led the Lunar Revolution on time line three, code 'Neil Armstrong.' Let's skip the details; it's all in Encyclopedia Galacta (sic) and other books."
In Arthur C. Clarke's and Gentry Lee's novel Rama II (1989), Nicole des Jardins says to Richard Wakefield, "Just think, the sum of everything all human beings know or have ever known might be nothing more than an infinitesimal fraction of the Encyclopedia Galactica."
There was a series of five video documentaries entitled Encyclopædia Galactica in 1993, with the titles “The Inner Solar System”, “The Outer Solar System”, “Star Trekking”, “Discovery”, and “Astronomy and the Stars”. The videos were produced by York Films of England and distributed by Encyclopædia Britannica (Australia). Other entities associated with the production of the video series were Encyclopædia Britannica Educational Corporation, The Learning Channel, The Discovery Channel Europe, S4C Wales, System TV France and Yleisradio Finland.
There was an Encyclopedia Galactica: from the Fleet Library aboard the Battlestar Galactica published in 1978. Aimed at a juvenile audience, this was a tie in to the Battlestar Galactica television series being broadcast at the time.
The term has been used in non-fictional contexts as well. One example is its use by Carl Sagan (1934–1996) in his 1980 book Cosmos, and his documentary video series of the same name, to refer to a text where hypothetical extraterrestrial civilizations could store all of their information and knowledge.