Many sound patterns in languages are cases of fossilized coarticulation, that is, synchronic or phonetic contextual variation became diachronic or phonological variation via sound change. An examination of languages' phonologies can therefore yield insights into the mechanisms of coarticulation. In this paper I discuss (a) the need to differentiate between phonological processes that are and are not due to coarticulation, (b) the need to differentiate between ‘on-line’ synchronic variation and comparable fossilized diachronic variation, (c) how to determine some of the constraints on coarticulation – especially the higher priority of maintaining acoustic-auditory, rather than articulatory, norms for the shape of speech elements, and (d) how coarticulation presents a “parsing” problem to the listener and, of course, to systems for automatic speech recognition.