Among the most discussed immigrants of the postwar period are those many believe have never actually arrived—aliens from other worlds. For many these stories are the stuff of science fiction—where an alien threat has remained big box office from The Thing (1952; 1982) and War of the Worlds (Orson Welles’ radio version 1938; film 1953) through Close Encounters of the Third Kind (1977) and E.T. (1982) to Independence Day (1997) and Men in Black (1998). American scientists, military and government agencies have generally concurred in rejecting any such possibilities. Yet, other Americans assemble sightings, photographs, personal testimonies, reinterpretations of historical texts and material evidence to prove alien contact, covered up by a vast government conspiracy (as in television’s The X-Files). Indeed, whether to treat such evidence as incitement to further research or signs of mass hysteria continues to divide analysts.

Despite many earlier science-fiction accounts of extra-terrestrial life and alien arrivals, clear changes arrived in the Cold War era. Pilot Kenneth Arnold’s report of a formation of incredibly fast blue-white objects over Washington’s Cascade mountains on June 24, 1947 is generally taken as inaugurating the modern UFO era (Unidentified Flying Objects; more popularly, “flying saucers”). This incident was followed on July 2 by reports of a UFO crash in Roswell, New Mexico, later dismissed by the government as a weather balloon; skepticism here makes Roswell critical for later ufologists. Thousands of reports followed, forcing an air force investigation, Project Blue Book, from 1948 to 1969. By 1953, the CIA-sponsored Robertson Panel concluded that UFOs did not exist, but that stories about them threatened national security; after August 1953, reports became classified. Yet, in a few months, Donald Keyhoe’s bestselling Flying Saucers from Outer Space (1953) restated these claims and debate has never disappeared since.

Intense sightings in 1957 and 1973, for example, showed the liveliness of saucers and watchers.

Various genres of UFO narratives complicate evaluations of evidence. Reports (and photographs) of bright lights and unusual movements have tended to be explained as other airborne objects or reflections or weather phenomena, without convincing skeptical audiences. Contact has been more problematic. The type case for alien abduction was Betty and Barney Hill’s hypnosis-induced narrative of a 1961 abduction. Examination of abduction narratives as factual evidence by professors David Jacobs (Temple) and John Mack (Harvard Medical School) has created subsequent firestorms in academic communities (see Secret Life, 1992). T. Matheson, by contrast, in Alien Abductions (1998) reads these stories as the emergence of a new mythology. Others have related such narratives to anxieties of changing roles of Americans and whites in a global economy.

Analysis of UFOs diverges from a scientific search for extra-terrestrial intelligence (SETI), spurred on in the 1970s by Carl Sagan and distinguished researchers. Whether or not Earth has been visited, this project assumes, others may still be there. Space flights have included materials to establish contact with such beings.

It is tempting to read extra-terrestrial beings as symbols of race, class and change (developed by the film Alien Nation, 1988, which depicted massive extra-terrestrial arrivals through analogies with African Americans and recent refugees). Yet, other Americans read them as truth, personal experiences or symbols of conspiracy, a theme of vocal debate on the Internet.