Each year, the Interagency Autism Coordinating Committee (IACC) releases a list of scientific advances that represent significant progress in the field of autism research. The "2021 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 2021 have provided new insight into disparities in screening, medication use in autism, and the biology associated with communication outcomes. The advances also include studies that investigated early interventions and family navigation, service needs across the lifespan, and updated prevalence estimates across demographic groups. Articles in the "Summary of Advances" are grouped according to the topics represented by the seven Questions of the "2016-2017 IACC Strategic Plan for ASD." Citations for the articles selected for the "Summary of Advances," as well as a complete listing of those nominated, are included at the end of the document. [For the 2020 Summary, see ED623991.]