Before the onset of sensory experience, spontaneous correlated activity plays a key role in the refinement of neuronal circuits within developing mammalian sensory systems. In the auditory system, sound frequency is encoded by the place of hair cells along the length of the cochlea. The precise tonotopic arrangement of neuronal connectivity in the auditory pathway is thought to be established by spontaneous activity that is synchronous among groups of hair cells along the length of the cochlea during early postnatal development. In this lecture, we will discuss the nature of the spontaneous activity observed in the developing auditory system.