The Foundation universe describes a future history of humanity's colonization of the galaxy, spanning nearly 25,000 years, created through the gradual fusion of the Robot, Galactic Empire, and Foundation book series written by American author Isaac Asimov.

The Foundation series is set in the same universe as Asimov's first published novel, Pebble in the Sky, although Foundation takes place about 10,000 years later. Pebble in the Sky became the basis for the Galactic Empire series. Then, at some unknown date (prior to writing Foundation's Edge) Asimov decided to merge the Foundation/Galactic Empire series with his Robot series. Thus, all three series are set in the same universe, giving them a combined length of 18 novels, and a total of about 1,500,000 words. The merge also created a time-span of the series of around 20,000 years.

The Stars, Like Dust states explicitly that the Earth is radioactive because of a nuclear war. Asimov later explained that the in-universe reason for this perception was that it was formulated by Earthmen many centuries after the event, and which had become distorted, due to the loss of much of their planetary history.^{[citation needed]} This work is generally regarded as part of the Empire series, but does not directly mention either Trantor or the other Spacer worlds. One character is said to have a Visi-Sonor, the same musical instrument that is played by the clown Magnifico in Foundation and Empire.

Asimov integrated the Robot series into his all-encompassing Foundation series, making the robot R. Daneel Olivaw appear again twenty thousand years later in the age of the Galactic Empire, in sequels and prequels to the original Foundation trilogy; and in the final book of the Robots series, Robots and Empire, Asimov describes how the worlds that later formed the Empire were settled, and how Earth became radioactive (which was first mentioned in Pebble in the Sky).

The stand-alone novel Nemesis is also in the same continuity; being referenced in Forward the Foundation, where Hari Seldon refers to a twenty-thousand-year-old story of "a young woman that could communicate with an entire planet that circled a sun named Nemesis". Commentators noted that Nemesis contains barely disguised references to the Spacers and their calendar system, the Galactic Empire, and even to Hari Seldon which seem to have been deliberately placed for the purpose of later integration into the Foundation universe.

The foreword to Prelude to Foundation contains the chronological ordering of Asimov's science fiction books. Asimov stated that the books of his Robot, Empire, and Foundation series "offer a kind of history of the future, which is, perhaps, not completely consistent, since I did not plan consistency, to begin with." Asimov also noted that the books in his list "were not written in the order in which (perhaps) they should be read". In the Author's Note, Asimov noted that there is room for a book between Robots and Empire and The Currents of Space, and that he could follow Foundation and Earth with additional volumes.

Forward the Foundation, Nemesis, and The Positronic Man do not appear in Asimov's list, as they were not yet published at the time, and the order of the Empire novels in Asimov's list is not entirely consistent with other lists. For example, the 1983 Ballantine Books printing of The Robots of Dawn lists the Empire novels as: The Stars, Like Dust, The Currents of Space, and Pebble in the Sky. Given that The Currents of Space includes Trantor and that The Stars, Like Dust does not, these two books possibly were accidentally reversed in Asimov's list.

While not mentioned in the "Author's Note" of Prelude to Foundation, the novels The End of Eternity (1955), Nemesis (1989), and The Positronic Man (1992) (written by Robert Silverberg) are related to the greater Foundation series.