The article presents the classification and key features of the most important language functions. Consideration of the leading position of bio-cognitive science that language cognition is associated with functioning of the entire human nervous system necessitates specifying the leading functions of language. The list of language functions has been continued with a generalizing invariant function which is a generalized meaningful core of the whole lexical structure of a word, formed by a native speaker over time, which allows them to have good situation awareness. A figurative fantasy function presented in the article is meant to provide a link between language and imagination by sparing consciousness copresence. The article reflects the scholarsí controversy concerning the determination of a key function of language. A communicative function of language is replaced by an adaptive one with ever increasing frequency, and language capacity is considered as a biological property of a living organism. The adaptive function of language implies the modification of the behavior of communicants such that the reality provides them with the best conditions for interaction. A communicant modifies their speech behavior, enhancing their general adaptational capacity in the surrounding. Thus, linguistic signs perform the function of orienting toward a more effective type of interpersonal interaction. The method of analytical reconstruction made it possible to obtain a systematic understanding of verbal and cogitative processes and conceptualization of semantic experience through the prism of understanding the functions of language.Keywords: language functions, adaptive function of language, communication process, cognitive linguistics, bio-cognitive science.