This contribution discusses the role of language variation in explaining mutual adaptation in interactive communication. Variability is one of the most fundamental and pervasive facets of language (and other communicative means) and lies at the heart of interactive adaptation – as the variety of linguistic means to express a particular idea that exists within and between communicators both allows for and necessitates adaptation. Examples from both sociolinguistic and psycholinguistic approaches to the study of linguistic variation are provided. It is argued that the forming new theory of communication needs to combine both perspectives and to build onto empirical results from both lines of research, focusing both on socially meaningful variation and on the individual mechanisms and mental representations involved in linguistic choices.