The purpose of this Funding Opportunity Announcement (FOA) is to encourage grant applications for the support of research designed to elucidate the diagnosis, epidemiology, etiology, genetics, treatment, and optimal means of service delivery in relation to Autistic Disorder ("autism") and autism spectrum disorders (Rett's Disorder, Childhood Disintegrative Disorder, Asperger's Disorder, Pervasive Developmental Disorder-Not Otherwise Specified, or "Atypical Autism"). This FOA is meant to support the broad research goals of the Autism Research Matrix (http://www.nimh.nih.gov/autismiacc/researchmatrix.pdf). In February 2003, Congress requested that the Department of Health and Human Services (HHS) develop a set of autism research goals and activities for the next several years (House Report 109-10). Input into this activity included a meeting of autism investigators with a range of scientific expertise, as well as input from community members. Preparation for specifying this matrix involved a two-day meeting of an expert panel of scientists; public presentation and discussion of a draft matrix at the Autism Summit Conference in Washington DC on November 20, 2003; and adoption of the matrix by the Federal Interagency Autism Coordinating Committee (IACC).