Decades of research and practice in social and emotional development have left us with a body of knowledge that tells us that (1) social, emotional, and cognitive development are intertwined in the brain and in behavior and influence school and life outcomes; (2) social, emotional, and cognitive skills and competencies grow in supportive relationships and are influenced by experience and context; and (3) there are programs and practices that have been shown to be effective in supporting these skills and competencies. The science of social and emotional learning is distinct in that it represents a blend of the developmental and applied sciences. In this article, we summarize a key framework that has guided much of the research and practical work of social and emotional learning, and we synthesize the major areas of research that have propelled the field forward. We then turn to what's next, describing and illustrating 4 essential principles that should guide work in the future.