The extraterrestrial hypothesis is the idea that some UFOs are vehicles containing or sent by extraterrestrial beings (usually called aliens in this context). As an explanation for UFOs, ETI is sometimes contrasted with EDI (extradimensional intelligence), for example by Allen Hynek.
- "The search for ET is a detective story without a body" by Nigel Henbest, New Scientist, March 9, 2013, p. 53.
- Fuller, Curtis (1980). Proceedings of the First International UFO Congress. New York: Warner Books., pp. 157-63.