Each year, the Interagency Autism Coordinating Committee (IACC) releases a list of scientific advances that represent significant progress in the field. The "2019 IACC Summary of Advances" provides short, plain language summaries of the top research breakthroughs selected by the IACC from a pool of research articles nominated by the members. The 20 studies selected for 2019 have provided new insight into disparities in autism spectrum disorder (ASD) diagnoses, predictors of language development in preschoolers with ASD, and the impact of various environmental factors on ASD risk. The advances also include studies of behavioral interventions for children with ASD, strategies to train therapists in publicly funded mental health services, supports for transition-age youth and young adults, and ASD prevalence estimates in 4-year-old children. Articles in the "IACC Summary of Advances" are grouped according to the topics represented by the seven questions of the "IACC Strategic Plan for ASD": (1) How can I recognize the signs of ASD, and why is early detection so important?; (2) What is the biology underlying ASD?; (3) What causes ASD, and can disabling aspects of ASD be prevented or preempted?; (4) Which treatments and interventions will help?; (5) What kinds of services and supports are needed to maximize quality of life for people on the autism spectrum?; (6) How can we meet the needs of people with ASD as they progress into and through adulthood?; and (7) How do we continue to build, expand, and enhance the infrastructure system to meet the needs of the ASD community? Citations for the articles selected for the "2019 IACC Summary of Advances," as well as a complete listing of those nominated, are included at the end of the document. [For the 2018 Summary, see ED598984.]