Cochlear implantation allows prelingually and postlingually deafened patients to achieve meaningful auditory sensation and speech understanding. Since the introduction of the cochlear implantation in clinical practice, a wide spectrum of factors known to affect postimplantation performance had been identified. Despite extensive research, the considerable variability in postoperative performance is still incompletely understood. Proper knowledge of these factors not only improves clinician’s predictive accuracy but may also reveal factors that can be manipulated to achieve optimal performance.