The development and improvement of cochlear auditory prostheses have radically reshaped the management of children and adults with significant hearing loss. Rapid evolution in the candidacy criteria and the technology has resulted in a large number of individuals who have benefited from implantation. Cochlear implants replace the normal inner ear by transforming acoustic sound signals into electric stimuli and deliver them to the auditory nerve. The decision to implant in a patient is a medical and surgical one. Candidacy issues, device selection, and planning for postoperative rehabilitation are complex, which require a dedicated cochlear implant team. Medical and surgical evaluation includes all aspects of cochlear implant candidacy, including critical analysis of hearing tests, motivation of the patient and family, and status of language development. Postoperative speech recognition results are variable. The expected results depend heavily on the environment in which cochlear implants are used, as well as on case selection. In children, implantation before the age of 2 years provides a distinct advantage over later implantation in cases of early-onset deafness. Postimplantation rehabilitation can be important for some adult implant recipients, but appears to be critical for children to optimize the usefulness of an implant. For early diagnosis of neonatal deafness and early implantation, a national neonatal hearing screening program is mandatory.