The majority of children from birth to age 5 in the United States regularly attend ECE programs. There are many types of ECE in the United States. Some are publicly funded, such as the federal Head Start and Early Head Start programs and state-funded pre-kindergarten. Others are privately funded community-based businesses such as home-based and center-based child care. Given the substantial time that young children spend in ECE, it is important that parents and policymakers understand how ECE supports children’s development and learning. In this brief, we summarize the research evidence on how high-quality ECE benefits all young children, as well as key subgroups, such as children who are dual language learners and children with disabilities. We also explain the specific features of high-quality ECE that research finds are most important for children’s development. Finally, we provide details about the research evidence summarized in this brief. (author abstract)