The term "cyborg" was first used by Norbert Weiner in 1947. A cyborg is a being who is a mixture of organic and cybernetic (bionic) parts. The term cyborg is short for "cybernetic organism."

Kurt Vonnegut's Player Piano (1952) describes a cybernetic system. In "The Cybernetic Brain" (1950), Raymond F. Jones described human brains integrated into a computer, as do Frederik Pohl and C.J. Kornbluth in Wolfbane (1959), Chris Boyce in Catchworld (1975), and William Hjortsberg in Grey Matters (1971). Earlier examples of cyborgs in science fiction are E.V. Odle's The Clockwork Man (1923), Edmond Hamilton's "The Comet Doom" (1928), Curt Siodmak's Donovan's Brain (1943), and C.L. Moore's "No Woman Born" (1944).

The concept of turning a human being into a cyborg was proposed by Manfred Clynes and Nathan Kline in 1960 for space exploration. They envisioned a human altered to permit him to survive in extraterrestrial environments, as did Frank Robinson in his Mars series of novels. Cordwainer Smith's "Scanners Live in Vain" (1950) deals with men who are given mechanical parts to withstand the pain of space, as does Vonda McIntyre's Superluminal (1983).

One type of cyborg for space exploration is a human integrated with mechanical parts but still in a conventionally shaped humanoid body. The other cybernetic method of space exploration proposed by SF writers was to integrate a human (either the entire body or just the brain and central nervous system) directly into a spaceship. Examples include Thomas N. Scortia's "Sea Change" (1956), Anne McCaffrey's The Ship Who Sang (1969), Frederik Pohl's Man Plus (1976), and Gordon Dickson's The Forever Man (1986).

One can argue that any human enhanced with mechanical components is a cyborg. By that definition, a cardiac patient with a pacemaker is a cyborg. So is the person with an artificial leg. So is a pet dog with a chip implanted under his skin so he can be electronically tracked if missing.

Bernard Wolfe suggested that people might replace their limbs with prosthetics in Limbo (1952), as did Martin Caidin in Cyborg (1972), which was made into the TV series The Six-Million Dollar Man (see chapter on Bionics).