X Minus One is an American half-hour science fiction radio drama series that was broadcast from April 24, 1955, to January 9, 1958, in various timeslots on NBC. Known for high production values in adapting stories from the leading American authors of the era, X Minus One has been described as one of the finest offerings of American radio drama and one of the best science fiction series in any medium.

Radio drama is a dramatized, purely acoustic performance. With no visual component, radio drama depends on dialogue, music and sound effects to help the listener imagine the characters and story: "It is auditory in the physical dimension but equally powerful as a visual force in the psychological dimension." Radio drama includes plays specifically written for radio, docudrama, dramatized works of fiction, as well as plays originally written for the theatre, including musical theatre, and opera.