The term xenology derives from the Greek xenos, which as a substantive has the meaning "stranger, wanderer, refugee" and as an adjective "foreign, alien, strange, unusual."
The first full-length book on the subject was written in 1979 by Robert A. Freitas Jr., who argued for the primacy of the term in the context of extraterrestrial life in a 1983 letter to the journal Nature.
It is used to denote a hypothetical science whose object of study would be extraterrestrial societies developed by alien lifeforms. In science fiction criticism and studies the term has been advocated by writers such as David Brin ("Xenology: The New Science of Asking 'Who's Out There?'" Analog, 26 April 1983) as an analogue of (terrestrial) ethnology. By extension the term may also refer to the fictional creation of "alternative humankinds", that is, human cultures and societies that have evolved on alien worlds. Science fiction writers who have created such xenological fictions include Poul Andersen, Jack Vance, Ursula Le Guin, Joanna Russ, and Donald Kingsbury. Writers who have explored alien rather than human xenologies include Orson Scott Card, Chad Oliver and C. J. Cherryh. Often, science fiction may combine human and alien xenologies, one good example being Jack Vance's Tschai series of novels, in which an interplanetary traveller from Earth is stranded on a planet dominated by four technically and culturally sophisticated alien species and a number of human societies, which, having been abducted and taken there during prehistory, have evolved in ways determined by the influence of their more powerful non-human masters.
Instances in which Xenology was referred to in a work of Science Fiction include the Brothers Strugatsky's 1972 novel "Roadside Picnic." In section three of which one of the character's, a noble laureate by the name of Valentine Pillman, explains Xenology as "an unnatural mixture of science fiction and formal logic. At its core is a flawed assumption—that an alien race would be psychologically human."