The goal of this research is to create a screening tool that will have strong sensitivity and specificity in identifying infants in their 8th through 15th month who will eventually have a diagnosis of autism spectrum disorder (ASD). This project will extend the investigators' previous work with the First Year Inventory (FYI), which is currently being used to screen infants who are 11.5 to 12.5 months old, and make it into a First Years Inventory (FYI). The FYI 3.0 incorporates recent findings regarding atypical behaviors in infants who will eventually have a diagnosis. More importantly, 9 infants who have been identified in the original cohort and screened at 12 months eventually were diagnosed with ASD, 120 developed other problems, and 569 are developing typically. These data allow for refinement of the original questions and gain better leverage on distinguishing ASD from other problems. The first aim in the present project is to obtain the normative data needed to create a developmentally sensitive risk metric. The second aim is to assess the normative cohort at 24 and 36 months to screen for symptoms of ASD and thus obtain a preliminary estimate of the FYI 3.0's sensitivity and specificity. A tool that identifies infants at risk for an eventual diagnosis of autism will facilitate research on the etiology of ASD, allow identification of children in the general population who might benefit from early intervention, support empirical tests of early interventions, and enable primary care practitioners to assess risk for ASD during routine well-baby checkups.