Biophysical music is a rapidly emerging area of electronic music performance. It investigates the creation of unconventional computing interfaces to directly configure the physiology of human movement with musical systems, which often are improvisational and adaptive. It draws on a transdisciplinary approach that combines neuromuscular studies, phenomenology, real-time data analysis, performance practice and music composition. Biophysical music instruments use muscle biosignals to directly integrate aspects of a performer’s physical gesture into the human–machine interaction and musical compositional strategies. This chapter will introduce the principles and challenges of biophysical music, detailing the use of physiological computing for musical performance and in particular the musical applications of muscle-based interaction.