Terraforming in science fiction is the modification of existing worlds to be fitting homes for human beings. Oftentimes, a familiar planet of our solar system, such as Mars or Venus, is terraformed, but far-off planet, asteroids, and the moons of gas giants are all

First seen as an element of setting in James B. Alexander's 1909 The Lunarian Professor and His Remarkable Revelations Concerning the Earth, the Moon, and Mars; Together with an Account of the Cruise of the Sally Ann, terraforming was a dominant subtext of Stapledon's Last and First Men, wherein descendents of modern man seek a new home for a doomed human race.

Terraforming as a central theme of sf literature came into being with Kim Stanley Robinson's works, anchored by the Mars trilogy.

Terraforming is modern science fiction's mouthpiece for both utopianism and a Green sense of ecological responsibility.