The narrator is a London businessman who withdraws to the countryside to write a play, by which he hopes to alleviate his financial problems. Bedford rents a small countryside house in Lympne, in Kent, where he wants to work in peace. He is bothered every afternoon, however, at precisely the same time, by a passer-by making odd noises. After two weeks Bedford accosts the man, who proves to be a reclusive physicist named Mr. Cavor. Bedford befriends Cavor when he learns he is developing a new material, cavorite, which can negate the force of gravity.

When a sheet of cavorite is prematurely processed, it makes the air above it weightless and shoots off into space. Bedford sees in the commercial production of cavorite a possible source of "wealth enough to work any sort of social revolution we fancied; we might own and order the whole world". Cavor hits upon the idea of a spherical spaceship made of "steel, lined with glass", and with sliding "windows or blinds" made of cavorite by which it can be steered, and persuades a reluctant Bedford to undertake a voyage to the moon; Cavor is certain there is no life there.

On the way to the moon, they experience weightlessness, which Bedford finds "exceedingly restful". On the surface of the moon the two men discover a desolate landscape, but as the sun rises, the thin, frozen atmosphere vaporizes and strange plants begin to grow with extraordinary rapidity. Bedford and Cavor leave the capsule, but in romping about get lost in the rapidly growing jungle. They hear for the first time a mysterious booming coming from beneath their feet. They encounter "great beasts", "monsters of mere fatness", that they dub "mooncalves", and five-foot-high "Selenites" tending them. At first they hide and crawl about, but growing hungry partake of some "monstrous coralline growths" of fungus that inebriate them. They wander drunkenly until they encounter a party of six extraterrestrials, who capture them. The insectoid lunar natives (referred to as "Selenites", after Selene, the moon goddess) are part of a complex and technologically sophisticated society that lives underground, but this is revealed only in radio communications received from Cavor after Bedford's return to earth.