Sound change is one of the oldest areas of linguistic inquiry but also today an area of vibrant and rapid progress. Current work pursues several very different lines of investigation, including formal phonology, phonetics and variationist theories and methods. In this talk, we argue for the need to integrate phonological theory and phonetics in new ways to understand sound change while taking seriously the notion of ‘structured heterogeneity’. Concretely, speech sounds have clear fundamental structures but also show vast variability, as successive generations of learners and speakers build grammars from rich and diverse input. We draw case studies from laryngeal contrasts, rhotics and vowel systems. In all, we find remarkable variability on the surface, but with fundamental stability in abstract structure. A clearer picture of sound change emerges through investigation and analysis of both the ‘structure’ and the ‘heterogeneity’ of sound patterns.