We are investigating the development and re-organization of the human central pathways in congenitally deaf children who regain hearing after being fitted with cochlear implants. Our measures of cortical development include cortical auditory evoked potentials (CAEP), high density electroencephalography (EEG), magnetoencephalography (MEG) and behavioral responses to auditory, visual, auditory-visual and somatosensory stimulation in the developing brain. In a series of experiments we have established the existence of, and time limits for, a sensitive period for normal development of auditory cortical pathways after cochlear implantation. Cochlear implantation within the sensitive period results in near-normal development of central auditory pathways. When children are implanted after the sensitive period, we find evidence of cortical re-organization. In late-implanted children, somatosensory and visual stimuli activate higher-order auditory areas and processing of auditory stimuli (like speech) involves multimodal areas such as parieto-temporal cortex. Late implanted children show significant deficits in unimodal (A-only & V-only) and multimodal (AV) behavioral processing compared to early-implanted and normal-hearing children. Overall, our results suggest that cortical re-organization occurs after a relatively brief period of deafness early in childhood. Cochlear implantation into a re-organized cortex does not appear to reverse the deficits in multimodal integrative processing caused by sensory deprivation.