This chapter introduces neurophysiological evidence on the dissociation between unconscious and conscious aspects of musical sound perception. The focus is on research conducted with the event-related potential (ERPevent-relatedpotential (ERP)) technique, which allows chronometric investigation of information-processing stages during music listening. Findings suggest that automatic processes are confined to the auditory cortex and might even involve the discrimination of deviations from simple musical scale rules. In turn, voluntary, cognitive processes, likely originating from the inferior prefrontal cortex, are necessary to understand more complex musical rules, such as tonality and harmony. The implications of understanding how and to what extent music is processed below the level of consciousness are discussed in rehabilitation and therapeutic settings.