Several research areas, notably those of psychology, physiology, and ethology, are reviewed in order to construct an interdisciplinary picture of problems and concepts pertaining to neurobehavioral development. Genetic factors, pre- and post-natal experiences and environmental influences which may affect ontogeny and modify the behavioral phenotype are reviewed. Development is considered as a series or continuum of genotype-environment interactions, and the effects of self-stimulation, experiential deprivation, enrichment, and "handling" are discussed. Ontogenetic phenomena, such as heterochronous patterning, induction and canalization, socialization, exploration and motivation, and the relationship between ontogeny and phylogeny of behavior are detailed to exposes the dynamic and intrinsic complexities of neurobehavioral development and of the genotype-environment interaction.