Mammalian ears evolved to provide exquisite sensitivity for detection and discrimination of sounds. Along the evolutionary path, self-repair ability diminished, such that most injuries become irreparable and lead to permanent hearing loss. Innovative therapies are being developed to restore the inner ear and provide hearing ability to deaf patients. Among the biological options for future therapies are the implantation of stem cells or the induced transformation of non- sensory cells to new sensory (hair) cells. Therapies for nerve regeneration are also being developed in order to enhance performance with the cochlear implant and to innervate stem cells. Bio-engineering approaches which combine such biological therapies with artificial sources of acoustic stimulation are another area of intense development.