Cochlear implant: A small complex electronic device that is surgically placed (implanted) within the inner ear to help persons with certain types of deafness to hear. Cochlear implants rarely cure severe or profound deafness but they can help some hearing-impaired people to distinguish the sounds of language clearly enough to participate in a verbal environment. For children who are congenitally deaf (born deaf), a cochlear implant can markedly increase the child's chance of being able to function effectively in mainstream school classes.

A cochlear implant has four basic parts: a microphone, which picks up sound from the environment; a speech processor, which selects and arranges sounds picked up by the microphone;a transmitter and receiver/stimulator, which receive signals from the speech processor and convert them into electric impulses; and electrodes, which collect the impulses from the stimulator and send them to the brain. Whereas hearing aids amplify sound, cochlear implants compensate for damaged or non-working parts of the inner ear. A cochlear implant electronically finds useful sounds and then sends them to the brain.

Deaf children who receive cochlear implants in infancy tend to have neurological development closest to that of hearing children. Adults who have lost all or most of their hearing later in life may also benefit from cochlear implants. These older candidates can often associate the sounds made through an implant with sounds they remember. This may help them to understand speech without visual cues or systems such as lipreading or sign language.