The mechanical response of the basilar membrane in the cochlea plays a fundamental role in human hearing. This volume discusses the main aspects of cochlear compression, including anatomy and physiology; the perceptual consequences of compression in normal hearing; the effects of hearing loss on compression; and its function in hearing aids and cochlear implants. The role of compression has increasing practical significance as it is incorporated into hearing aids and cochlear implants to compensate for inadequate compression in people with cochlear hearing loss.