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.