Due to its aerodynamic, articulatory, and acoustic complexities, the fricative /s/ is known to require high precision in its control, and to be highly resistant to coarticulation. This study documents in detail how jaw, tongue front, tongue back, lips, and the first spectral moment covary during the production of /s/, to establish how coarticulation affects this segment. Data were obtained from 24 speakers in the Wisconsin x-ray microbeam database producing /s/ in prevocalic and pre-obstruent sequences. Analysis of the data showed that certain aspects of jaw and tongue motion had specific kinematic trajectories, regardless of context, and the first spectral moment trajectory corresponded to these in some aspects. In particular contexts, variability due to jaw motion is compensated for by tongue-tip motion and bracing against the palate, to maintain an invariant articulatory-aerodynamic goal, constriction degree. The change in the first spectral moment, which rises to a peak at the midpoint of the fricative, primarily reflects the motion of the jaw. Implications of the results for theories of speech motor control and acoustic-articulatory relations are discussed.