<![CDATA[Register and genre are central concepts for explaining how language varies with situation and purpose, yet they are studied in separate traditions, including systemic functional linguistics, genre analysis, corpus linguistics, clinical discourse research and natural language processing, which rarely inform one another. The rapid growth of digital texts and large language models has made the question of how linguistic variation is organised newly urgent. This narrative review aimed to synthesise recent research on register and genre across these traditions and to examine what it suggests about the relationship between linguistic variation, meaning-making and language processing. Foundational works and recent empirical studies, mainly published between 2015 and 2025, were identified through searches of Google Scholar, DOAJ and the ACL Anthology and synthesised thematically. Three themes emerged. First, registers are identified by co-occurring lexical and grammatical features that vary along a continuum rather than by fixed rules, and readers' and listeners' expectations about genre shape how texts are processed. Second, genre functions as a framework for organising meaning, and explicit genre-based instruction consistently supports learners' writing development. Third, register and genre are increasingly applied beyond linguistics: discourse genre affects the language produced by speakers with and without aphasia, register and genre classification structures large web corpora, and register-based analyses reveal systematic differences between human and machine-generated texts. The review concludes that register and genre are best understood as flexible, usage-based systems that link linguistic form to social purpose. It also cautions that claims about their cognitive basis still rest on limited direct evidence and on research dominated by English.]]>
