The Expanse is a series of science fiction novels, and related novellas and short stories by James S. A. Corey, the joint pen name of authors Daniel Abraham and Ty Franck. The first novel, Leviathan Wakes, was nominated for the Hugo Award for Best Novel in 2012. The complete series was nominated for the Hugo Award for Best Series in 2017. It later won, following its second nomination for the same award in 2020.

The book series is made up of nine novels and nine novellas compiled in Memory's Legion. The series was adapted for television for Syfy, also under the title of The Expanse. When Syfy canceled the TV series after three seasons, Amazon Prime Video acquired it and produced three more seasons.

All novels and short works except the RPG exclusive short story have been released as audiobooks, with Jefferson Mays as the narrator for the novels and short works that include Drive, The Butcher of Anderson Station, The Vital Abyss, Strange Dogs, Auberon, and The Sins of Our Fathers. Erik Davies was originally the narrator for the novellas The Churn and Gods of Risk; but both have been re-released with Jefferson Mays narrating them as of December 28, 2021. While most of Memory's Legion is narrated by Jefferson Mays, the author's note portions are narrated by Daniel Abraham and Ty Franck.

The Expanse is set in a future in which, after the creation of the Epstein Drive, a fusion engine capable of producing continuous acceleration, humanity has colonized much of the Solar System (but does not have interstellar travel). The series initially takes place in the Solar System, using many real locations such as Ceres and Eros in the asteroid belt, the moons of Jupiter and Saturn, and small science bases as far out as Titania around Uranus, as well as well-established domed and underground settlements on Mars and the Moon, referred to as Luna.

At the series beginning, the governments of Earth (led by the United Nations) and Mars control the solar system in an uneasy military alliance, although substantial tensions exist between the two superpowers. Residents of the outer planets, living in stations built in the asteroid belt and the moons of Jupiter and Saturn, are referred to as "Belters". Due to the lack of gravity, they develop thin, elongated bodies, and have developed a creole language due to their physical isolation from Earth and Mars, with heavy influences from German and Chinese. Belters perform much of the gritty labor work to mine resources for the inner planets, which in turn control access to most necessary biological resources. As a result, substantial tensions exist between the Belt and the governments of Earth and Mars, proliferating itself through the existence of the Outer Planets Alliance, a fractured government and militant group that fights for Belter independence (labelled as a terrorist organization by the inner worlds).

As the series progresses, humanity gains access to thousands of new worlds by use of the rings, an artificially sustained wormhole network, created by a long-dead alien civilization. The ring in the Sol system is a thousand-mile diameter structure located two AU outside the orbit of Uranus. Passing through it leads to a hub of starless space approximately one million kilometers across, with more than 1,300 other rings, each with a star system on the other side. In the center of this hub, which is also referred to as the "slow zone" after the third novel, a highly defended alien space station controls the gates and can also set instantaneous speed limits on objects inside the hub as a means of defense.

The story is told through the points-of-view of many main characters. There are two POV characters in the first book and four in books two through five. In the sixth and seventh books, the number of POV characters increases, with several characters having only one or two chapters. The eighth book returned to a more limited number with five. In the final ninth book, there is an increase in POVs with some chapters having multiple POV characters. Every book also begins and ends with a prologue and epilogue told from a unique character's perspective, who will occasionally interject in the main body of the novel.

The central characters of The Expanse are the crew of the Rocinante, a salvaged Martian naval gunship.