Douglas Biber, Regents’ Professor of Applied Linguistics at Northern Arizona University, authors this article exploring the connections between register and a text-linguistic approach to language variation. He has spent the last 30 years pursuing a research program that explores the inherent link between register and language use, including at the phraseological, grammatical, and lexico-grammatical levels. His seminal book Variation across Speech and Writing (1988, Cambridge University Press) launched multi-dimensional (MD) analysis, a comprehensive framework and methodology for the large-scale study of register variation. This approach was innovative in taking a text-linguistic approach to characterize language use across situations of use through the quantitative and functional analysis of linguistic co-occurrence patterns and underlying dimensions of language use. MD analysis is now used widely to study register variation over time, in general and specialized registers, in learner language, and across a range of languages. In 1999, the Longman Grammar of Spoken and Written English (Biber et al.) became the first comprehensive descriptive reference book to systematically consider register variation in describing the grammatical and lexico-grammatical patterns of use in English. Douglas Biber’s quantitative linguistic research has consistently demonstrated the importance of register as a predictor of language variation. In his own words, “register always matters” (Gray 2013:?360, Interview with Douglas Biber, English Language & Linguistics).