The past two decades have been characterized by a growing body of research from diverse disciplines — child development, psychology, neuroscience, and economics, among others — demonstrating the importance of establishing a strong foundation in the early years of life. The research evidence has served to document the range of early childhood services that can successfully put children and families on the path toward lifelong health and well-being, especially those at greatest risk of poor outcomes. As early childhood interventions have proliferated, researchers have evaluated whether the programs improve children’s outcomes and, when they do, whether the improved outcomes generate benefits that can outweigh the program costs. This report examines a set of evaluations that meet criteria for scientific rigor and synthesizes their results to better understand the outcomes, costs, and benefits of early childhood programs. The authors focus on evaluations of 115 early childhood programs serving children or parents of children from the prenatal period to age 5. Although preschool is perhaps the best-known early childhood intervention, the study also reviewed such programs as home visiting, parent education, government transfers providing cash and in-kind benefits, and those that use a combination of approaches. The findings demonstrate that most of the reviewed programs have favorable effects on at least one child outcome and those with an economic evaluation tend to show positive economic returns. With this expanded evidence base, policymakers can be highly confident that well-designed and -implemented early childhood programs can improve the lives of children and their families.