The study of neurobehavioral development focuses on the mechanisms through which the experiences of an individual influence the ontogeny of brain circuits that ultimately control complex functions, such as social engagement, mood and emotional regulation and cognition. Advances in experimental approaches and technologies provide opportunities to gather more detailed information about developing behavioral systems. This information is more comprehensive and readily applied in studies utilizing strategies that link the disciplines of developmental neurobiology and psychology. Here, examples are provided to illustrate the hierarchical assembly of neural systems, which incorporate information from the genome and the environment to define the ultimate developmental trajectory of an individual. (Contains 2 figures.)