Cochlear implants have greatly been developed on last ten years. Their diversity makes their use and choice more complex. The authors expose simply the physiopathology of the implanted auditory system and basic principles of cochlear implants. Cochlear implants are caracterised by the number of channels and electrodes (monochannel, multichannel), the strategy of encoding (analogiq, digital), the transmission of signal (per-cutaneous, electro-magnetic induction), the site of stimulation (extra or intra-cochlear), the signal wave (sinusoid, pulse), the diffusion of current (monopolar, bipolar).