This talk will examine two specific human facets of new instrument design: sensorimotor skill and sociocultural factors. In the first case, it takes many years to achieve proficiency on an instrument, and a trained performer is unlikely to want to repeat the process afresh with an unfamiliar instrument. This talk will explore ways of designing new instruments which extend and repurpose existing expertise on familiar instruments. In the second case, instrumental performance is the locus of a rich set of aesthetic and social practices whose values should be considered at an early stage of any instrument design. The musical instrument thus takes on many different roles: as transducer of action to sound, as a mediator of the performer’s intentions, and as the product of a larger musical ecology.