This chapter will describe the development of the nervous system from the first neurons occurring around 17 days after conception until the end of puberty. The interaction between signaling factors in the environment, cell receptors, and transcription factors in the regulation of cell proliferation, cell differentiation, cell survival, and in the establishment of connections between neurons prior to birth will be described. It will be emphasized how functional connectivity in the nervous system develops through pruning mechanisms where only neurons and neuronal pathways which establish functionally effective connections with each other survive. This competitive regulation of connectivity (“survival-of-the-fittest connection”) is the basis of the ability of the immature brain to generate functional neural networks despite significant lesions early during development. The significance of environmental stimuli for optimal neurodevelopment during critical periods after birth and for efficient early interventions aiming to facilitate neurodevelopment will be discussed. The continued cognitive and motor development of children will be presented. The neuroplastic potential of the nervous system at different ages will be evaluated, and the challenges and possibilities that lesions at each of the developmental stages poses will be discussed.