Neuroscientists have long believed that there are sensitive periods in development during which the effects of experience play a critical role. And developmental psychologists have argued for the importance of early experience in the first years of life as being critical for brain and behavioral development. Most of the neuroscience research supporting these tenets was conducted with rodent or nonhuman primate models. Most of the work in human development is either correlational or has examined sensitive periods and early experience in sensory or perceptual systems. In this article, the authors present data from the Bucharest Early Intervention Project that supports the idea of sensitive periods affecting specific domains of development and the importance of early experience on brain and behavior.