Is there a distinction between New Interfaces for Musical Expression and New Interfaces for Controlling Sound? Thisarticle begins with a brief overview of expression in musical performance, and examines some of the characteristics ofeffective “expressive” computer music instruments. It becomes apparent that sophisticated musical expressionrequires not only a good control interface but also virtuosic mastery of the instrument it controls. By studying effective acoustic instruments, choosing intuitive but complexgesture-sound mappings that take advantage of established instrumental skills, designing intelligent characterizationsof performance gestures, and promoting long-term dedicated practice on a new interface, computer music instrumentdesigners can enhance the expressive quality of computer music performance.