The expansion of publicly-funded preschool education is currently the focus of a prominent debate. At present, 42% of 4-year-olds attend publicly funded preschool (28% attend public prekindergarten programs, 11% Head Start, and 3% special education preschool programs). A vigorous debate about the merits of preschool education is underway, although at times it has not included the most recent available evidence. The goal of this brief is to provide a non-partisan, thorough, and up-to-date review of the current science and evidence base on early childhood education (ECE). Our interdisciplinary group of early childhood experts reviewed rigorous evidence on why early skills matter, the short- and long-term effects of preschool programs on children's school readiness and life outcomes, the importance of program quality, which children benefit from preschool (including evidence on children from different family income backgrounds), and the costs versus benefits of preschool education. We focus on preschool (early childhood education) for four-year-olds, with some review of the evidence for three-year-olds when relevant. We do not discuss evidence regarding programs for 0-3 year olds.