The authors present some morphological, physiological and pathophysiological aspects of efferent system of innervation (i.e. olivocochlear system) of the organ of Corti. The cochlea is innervated by two different systems: 1) the medial efferent system which originates in the medial nucleus of the trapezoid body and synapses on outer hair cells, 2) the lateral efferent system which originates in the superior olivary nucleus and synapses on the dendrites of the auditory nerve under inner hair cells. An electrical stimulation as well as an acoustic stimulation of efferent fibers results in: a) suppression of the auditory nerve response (N1 amplitude reduction), b) increase in amplitude of cochlear microphonics and c) reduction of the endolymphatic potential. Due to presence of the crossed olivocochlear bundle, an ipsilateral stimulation of efferent fibers results in both ipsi- and contralateral response. Efferent fibers response is a feedback response to afferent fibers stimulation. There are some evidence that efferent system of innervation protects the cochlea against the effects of intense sound exposure.