The advent of modern neurobiological methods over the last three decades has provided overwhelming evidence that it is the interaction of genetic factors and the experience of the individual that guides and supports brain development. Brains do not develop normally in the absence of critical genetic signaling, and they do not develop normally in the absence of essential environmental input. The key to understanding the origins and emergence of both the brain and behavior lies in understanding how inherited and environmental factors are engaged in the dynamic and interactive processes that define and direct development of the neurobehavioral system. Neural Plasticity and Cognitive Development focuses on children who suffered focal brain insult (typically stroke) in the pre- or perinatal period which provides a model for exploring the dynamic nature of early brain and cognitive development. In most, though not all, of the cases considered, the injuries affect substantial portions of one cerebral hemisphere, resulting in patterns of neural damage that would compromise cognitive ability in adults. However, longitudinal behavioral studies of this population of children have revealed only mild cognitive deficits, and preliminary data from functional brain imaging studies suggest that alternative patterns of functional organization emerge in the wake of early injury. Neural Plasticity and Cognitive Development posits that the capacity for adaptation is not the result of early insult. Rather, it reflects normal developmental processes which are both dynamic and adaptive operating against a backdrop of serious perturbation of the neural substrate.