This paper provides an overview of effects of noise on the hearing system. Animal research has shown that excessive noise exposure results in decrease of blood flow in stria vascularis, alteration in permeability of ions in reticular lamina, swelling/rupture of hair cells, disarrangement or loss of stereocilia, broken tip links and side links between the stereocilia, swelling of afferent dentrides, rupture of the organ of Corti, decrease in tectorial membrane thickness, and increase in its compliance, etc. After the exposure, the stereocilia may become a fanlike structure or fuse together to form a giant stereocilia. In a severely damaged cochlea, the hair cells may be replaced by some undifferentiable scar tissue. The pharyngeal processes of the Deiter's cells and other supporting cells enlarge to seal off the endolymph and perilymph ion boundaries. The neural fibers and ganglion cells may gradually degenerate and tonotopic reorganization in dorsalcochlear nucleus follows. Along with these anatomical damages, physiological changes include disruption of the cochlear active process, changes in cochlear potentials, broadening of the turning curve of basilar membrane and spiral ganglion neurons, and hearing loss are also observed. Remedial procedures, e.g., regeneration of hair cells and ``preexposure conditioning`` are also discussed.