Is there a distinction between New Interfaces for MusicalExpression and New Interfaces for Controlling Sound? Thisarticle begins with a brief overview of expression in musicalperformance, and examines some of the characteristics ofeffective "expressive" computer music instruments. Itbecomes apparent that sophisticated musical expressionrequires not only a good control interface but also virtuosicmastery of the instrument it controls. By studying effectiveacoustic instruments, choosing intuitive but complexgesture-sound mappings that take advantage of establishedinstrumental skills, designing intelligent characterizationsof performance gestures, and promoting long-term dedicatedpractice on a new interface, computer music instrumentdesigners can enhance the expressive quality of computermusic performance.