The purpose of this Funding Opportunity Announcement (FOA) is to encourage research grant applications to support research designed to elucidate the etiology, epidemiology, diagnosis, and optimal means of service delivery in relation to Autism Spectrum Disorders (ASD). The R21 grant mechanism is intended to encourage exploratory/developmental research by providing support for the early and conceptual stages of project development. Exploratory, novel studies that break new ground or extend previous discoveries toward new directions are appropriate for this mechanism. No preliminary data are required but may be included if available.