Linguistic variation can roughly be defined as ‘different ways of saying the same thing’. This concept encompasses a very wide range of phenomena and sources of variation, including alternations and competing choices on the level of sounds, morphosyntax, lexicon and discourse, all of which can be conditioned by geographic, social, situational and individual factors. Traditionally, these phenomena have been dealt with by different branches of linguistics. For example, phonologists have dealt with with phonologically-conditioned variation on the level of sounds, grammarians with systematic variants and alternations in morphosyntax, stylisticians and discourse analysts with register and style variation, and sociolinguists with socially conditioned variants on different levels of language (as well as their relation to identity construction). The aim of my talk is to propose a unified framework bringing together all these perspectives on linguistic variation. This framework is part of my wider Entrenchment-and-Conventionalization Model (Schmid 2020), a usage-based sociocognitive dynamic complex-adaptive model of how language works in terms of structure, variation and change. One potential benefit of the model for explaining variation lies in the way in which it connects social processes and forces shaping conventionality in a speech community and cognitive processes and forces shaping the linguistic knowledge of individual speakers. I argue that providing a systematic picture of the social and cognitive foundations of linguistic variation will improve our understanding of the determinants and nature of variation and of its effects on identity construction and perception. My talk will consist of a theoretical and a practical part.