This special session discusses the issue if there is a biological grounding of phonology. By reviewing current and past work from different speech research disciplines we suggest that (1) biological factors provide the limits, the frame of reference for phonology, (2) phonology is shaped by optimization processes taking into account the nonlinear relations of different representations of speech (acoustics, articulation, speech perception), and (3) sociolinguistic factors and communicative usage affect, for instance, speech acquisition and sound change. The first of the three suggestions is biological in nature whereas the last represents the non-biological nature of speech.