Contactees are persons who claim to have experienced contact with extraterrestrials. Some claimed ongoing encounters, while others claimed to have had as few as a single encounter. Evidence is anecdotal in all cases. As a cultural phenomenon, contactees achieved their greatest notoriety during the 1950s, but individuals have continued to make similar claims. Some contactees have shared their messages with small groups of believers and followers, and many have written books, published magazine and newspaper articles, issued newsletters or spoken at UFO conventions. The accounts of contactees generally differ from those who allege alien abduction, in that while contactees frequently describe positive experiences involving humanoid aliens, abductees usually describe their encounters as frightening or disturbing.

Astronomer J. Allen Hynek described contactees thus:

The visitation to the earth of generally benign beings whose ostensible purpose is to communicate (generally to a relatively few selected and favored persons) messages of "cosmic importance". These chosen recipients generally have repeated contact experiences, involving additional messages

Contactees became a cultural phenomenon shortly after the modern era of UFO sightings began at the end of the 1940s. The contactees often gave lectures at UFO conventions and wrote books and articles about their alleged experiences. Though the contactee phenomenon peaked during the 1950s, it still exists today. Skeptics usually consider such "contactees" as charlatans, con artists or deluded in their claims. Susan Clancy wrote that such claims are "false memories" concocted out of a "blend of fantasy-proneness, memory distortion, culturally available scripts, sleep hallucinations, and scientific illiteracy".

Contactees usually portrayed aliens as more or less identical in appearance and mannerisms to humans. The aliens are also almost invariably reported as disturbed by the preponderance of violence, crime, and wars that occur on earth, and by the possession of various earth nations of nuclear and thermonuclear weapons. Curtis Peebles summarizes the common features of many contactee claims:

As early as the 18th century, people like Emanuel Swedenborg were claiming to be in psychic contact with inhabitants of other planets. 1758 saw the publication of Concerning Earths in the Solar World, in which Swedenborg detailed his alleged journeys to the inhabited planets. J. Gordon Melton notes that Swedenborg's planetary tour stops at Saturn, the furthest planet discovered during Swedenborg's era, he did not visit then-unknown Uranus, Neptune, or Pluto.

In 1891, Thomas Blott's book The Man From Mars was published. The author claimed to have met a Martian in Kentucky. Unusually for an early contactee, Blott reported that the Martian communicated not via telepathy, but in English.

George Adamski, who is probably the best-known UFO contactee of the 1950s, had an earlier interest in the occult, and in the 1930s founded the Royal Order of Tibet, a neo-theosophical organization. Michael Barkun wrote of Adamski: "His [later] messages from the Venusians sounded suspiciously like his own earlier occult teachings."