Project Summary/Abstract The ongoing goal of the Autism Biomarkers Consortium for Clinical Trials (ABC-CT) is to establish electroencephalography (EEG) and eye-tracking (ET) biomarkers that can be used for stratification and/or as sensitive and reliable objective assays related to social function in autism spectrum disorder (ASD) clinical trials. This renewal application seeks to further validate promising measures through three studies designed to enhance and extend the original ABC-CT study: (1) a confirmation study of the original findings in a new cohort using similar design (T1: Baseline, T2: 6 weeks post baseline, T3: 24 weeks post baseline) and sample size/characteristics (200 with ASD, 200 with typical development (TD)); (2) a follow-up study of the original cohort (N=399) to re-administer the biomarker and clinical batteries 2.5-4 years after original ABC-CT enrollment; (3) a feasibility study of parallel EEG and ET biomarkers in preschool-aged (3-5-year-old) children (25 with ASD, 25 with TD). The biomarker and clinical batteries measure key facets of social-communication in ASD using well- validated paradigms appropriate for the intended developmental and cognitive range. The study will rely on the same leadership and five Collaborating Implementation Sites (“Sites”) from the first phase, all highly experienced in multi-site collaborative clinical research using the proposed clinical, EEG, and ET methodologies. The Data Coordinating Core (DCC) will provide a secure informatics infrastructure for communication and data integration across the consortium to ensure organized data management, quality control, and reliable upload to the National Database for Autism Research (NDAR) and NIH Data Repositories. The Data Acquisition and Analysis Core (DAAC) will oversee consistent use of scientific standards and methodological rigor for data acquisition, processing, and analytics. The Administrative Core will oversee the operations of the sites, the DCC, and the DAAC to ensure methodologically and ethically rigorous, efficient completion of study aims and to coordinate with federal partners in this cooperative agreement by: 1) Coordinating communication and data sharing to manage all aspects of the project, including recruitment and data collection, data management and quality control, standardization of data acquisition and processing, analytic planning, and financial management; 2) Administering the consortium project across all sites and cores in terms of managing the central institutional review board, developing and disseminating Standard Operating Procedures, implementing Good Clinical Practice, maintaining research fidelity, overseeing quality control, and planning timely upload to NIH/NIMH Data Repositories; 3) Maintaining appropriate communication and integrating feedback from federal partners, executing the finalized protocol as per the collaborative agreement, and planning Steering Committee meetings and annual in-person meetings.