Exolinguistics (also called xenolinguistics and astrolinguistics) is the hypothetical (and fictional) study of the language of alien species. The nature and form of such languages remains purely speculative because so far no search for extra-terrestrial intelligence projects have detected signs of intelligent life beyond Earth. The possibility of future contact with intelligent extra-terrestrial life has made the question of the structure and form of potential alien language a topic of scientific and philosophical discussion.

A notable sub-genre of fictional languages are alien languages, the ones that are used or might be used by putative extra-terrestrial lifeforms. Alien languages are subject of both science fiction and scientific research.

Perhaps the most fully developed fictional alien language is the Klingon language of the Star Trek universe - a fully developed constructed language.

The problem of alien language has confronted generations of science fiction writers; some have created fictional languages for their characters to use, while others have circumvented the problem through translation devices or other fantastic technology.

Although this field remains largely confined to science fiction, the possibility of intelligent extra-terrestrial life makes the question of alien language a credible topic for scientific and philosophical speculation. While many cases an alien language is but an element of fictional reality, in a number of science fiction works the core of the plot are linguistic and psychological problems of communication between various alien races.

Fictional languages are constructed languages (conlangs) created as part of a fictional setting, for example in books or movies.

Fictional languages are intended to be the languages of a fictional world and are often designed with the intent of giving more depth and an appearance of plausibility to the fictional worlds with which they are associated, and to have their characters communicate in a fashion which is both alien and dislocated.

Some of these languages, e.g., in worlds of fantasy fiction, alternate universes, Earth's future, or alternate history, are presented as distorted versions or dialects of modern English or other natural language, while others are independently designed conlangs.

Fictional languages are separated from artistic languages by both purpose and relative completion: a fictional language often has the least amount of grammar and vocabulary possible, and rarely extends beyond the absolutely necessary. At the same time, some others have developed languages in detail for their own sake, such as JRR Tolkien's Quenya and Sindarin, Star Trek's Klingon language and Avatar's Na'vi language which exist as functioning, usable languages. Here "fictional" can be a misnomer.

By analogy with the word "conlang", the term conworld is used to describe these fictional worlds, inhabited by fictional constructed cultures. The conworld influences vocabulary (what words the language will have for flora and fauna, articles of clothing, objects of technology, religious concepts, names of places and tribes, etc.), as well as influencing other factors such as pronouns, or how their cultures view the break-off points between colors or the gender and age of family members.