The Encyclopedia Galactica is a fictional or hypothetical encyclopedia of a future galaxy-spanning civilization, containing all the knowledge accumulated by a society with trillions of people and thousands of years of history.
It was first used by Isaac Asimov in his novel Foundation, where it is central to the first part of the plot. Various people have since used the same idea, both in science and in science fiction. Douglas Adams' Hitchhiker's Guide to the Galaxy series frequently contrasts the Galactica with the presumably more popular Guide. For example, the introduction to the first book notes:
- 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 Encyclopedia 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.