Functional magnetic resonance imaging (fMRI) studies have had a profound impact on the understanding of the neurobiologic basis for autism and autism-spectrum disorders. Initial studies led to the delineation of many neural systems for brain–behavior relationships in ASD. Some relationships were previously well established, but others were elucidated in response to distinctive impairments in autism. This body of research clearly established autism and its signs and symptoms as being of neurologic origin, decomposed the unusual complex behavior into recognizable neural components, and established autism as a distributed neural systems disorder that disproportionately impaired many higher order abilities. The second phase of fMRI research in autism focused largely on the development of functional connectivity fMRI (fc-fMRI) methods and evidence that established autism as a disorder of underconnectivity among the brain regions participating in cortical networks. Supporting evidence of network dysfunction was provided by increased cerebral white matter volume on structural MRIs in very young but not older children with autism, accompanied by a diffuse increase in cortical gray matter volume. This constellation. together with other evidence, identified the cortical neuron(s) as the unit of dysfunction in autism. The growth dysregulation, i.e. early brain overgrowth followed by growth plateau, was classic evidence of disturbances in developmental neurobiologic events, specifically neuronal organizational events. Notably though, all developmental trajectories for brain growth are seen in autism, suggesting considerable heterogeneity in the specific underlying genetic mechanisms affected. With the discovery of about 20 mostly rare genes or gene mutations that are each involved in a molecular aspect of the development of neuronal connections, the fMRI and genetic findings in autism closed a loop that validated a developmental neurobiological based model of autism. Recent fMRI studies in autism focus on further articulation of functional connectivity disturbances, further delineation of the neural bases of deficits and skills, and delineation of disturbances in higher levels of brain organization related to control and regulation of thinking, feeling, and behaving.