First contact is a common theme in science fiction about the first meeting between humans and extraterrestrial life, or of any sentient species' first encounter with another one, given they are from different planets or natural satellites. It is closely related to the anthropological idea of first contact.

Popularized by the 1897 book The War of the Worlds by H. G. Wells, the concept was commonly used throughout the 1950s and 60s, often as an allegory for Soviet infiltration and invasion. The 1960s American television series Star Trek introduced the concept of the "Prime Directive", a regulation intended to limit the negative consequences of first contact.

Although there are a variety of circumstances under which first contact can occur, including indirect detection of alien technology, it is often portrayed as the discovery of the physical presence of an extraterrestrial intelligence. As a plot device, first contact is frequently used to explore a variety of themes.

Murray Leinster's 1945 novelette "First Contact" is the best known science fiction story which is specifically devoted to the "first contact" per se, although Leinster used the term in this sense earlier, in his 1935 story "Proxima Centauri".

The idea of humans encountering an extraterrestrial intelligence for the first time dates back to the second century AD, where it is presented in the novel A True Story by Lucian of Samosata. The 1752 novel Le Micromégas by Voltaire depicts a visit of an alien from a planet circling Sirius to the Solar System. Micromegas, being 120,000 royal feet (38.9 km) tall, first arrives at Saturn, where he befriends a Saturnian. They both eventually reach the Earth, where using a magnifying glass, they discern humans, and eventually engage in philosophical disputes with them. While superficially it may be classified as an early example of science fiction, the aliens are used only as a technique to involve outsiders to comment on Western civilization, a trope popular at the times.^{[citation needed]}

Traditionally the origin of the trope of conflict of humans with an alien intelligent species is attributed to The War of the Worlds by H. G. Wells, in which Martians mount a global invasion of Earth. Still, there are earlier examples, such as the 1888 novel Les Xipéhuz, a classic of French science fiction. It depicts the struggle of prehistoric humans with an apparently intelligent but profoundly alien inorganic life form. However in the latter novel it is unclear whether the Xipéhuz arrived from the outer space or originated on the Earth.

Throughout the 1950s, stories involving first contact were common in the United States, and typically involved conflict. Professor of Communication Victoria O'Donnell writes that these films "presented indirect expressions of anxiety about the possibility of a nuclear holocaust or a Communist invasion of America. These fears were expressed in various guises, such as aliens using mind control, monstrous mutants unleashed by radioactive fallout, radiation's terrible effects on human life, and scientists obsessed with dangerous experiments." Most films of this kind have an optimistic ending. She reviewed four major topics in these films: (1) Extraterrestrial travel, (2) alien invasion and infiltration, (3) mutants, metamorphosis, and resurrection of extinct species, and (4) near annihilation or the end of the Earth.

The 1951 film The Day the Earth Stood Still was one of the first works to portray first contact as an overall beneficial event. While the character of Klaatu is primarily concerned with preventing conflicts spreading from Earth, the film warns of the dangers of nuclear war. Based on the 1954 serialized novel, the 1956 film Invasion of the Body Snatchers depicts an alien infiltration, with the titular Body Snatchers overtaking the fiction town of Santa Mira. Similarly to The Day the Earth Stood Still, Invasion of the Body Snatchers reflects contemporary fears in the United States, particularly the fear of communist infiltration and takeover.