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 Research Project Grant (R01) mechanism supports discrete, specified projects based in scientific areas that represent the investigators specific interests and competencies, and that fall within the mission of the participating NIH Institutes and Centers (ICs). The proposed project must be related to the programmatic interests of one or more of the participating NIH Institutes and Centers (ICs) based on their scientific missions, and preliminary data are generally expected. Applicants pursuing exploratory/developmental research to support early and conceptual stages of project development should consider the companion R21 FOA, PA-21-200. Applicants pursuing secondary analysis of existing data, and pilot or feasibility studies that can be completed with limited budgets should consider the companion R03 FOA, PA-21-199.