Social and emotional learning (SEL) has become more central to education because of demand from educators, parents, students, and business leaders alongside rigorous research showing broad, positive impacts for students and adults. However, all approaches to SEL are not equal. Systemic SEL is an approach to create equitable learning conditions that actively involve all Pre-K to Grade 12 students in learning and practicing social, emotional, and academic competencies. These conditions require aligned policies, resources, and actions at state and district levels that encourage local schools and communities to build the personal and professional capacities of adults to: implement and continuously improve evidence-based programs and practices; create an inclusive culture that fosters caring relationships and youth voice, agency, and character; and support coordinated school-family-community partnerships to enhance student development. Promoting social and emotional competencies-including the abilities to understand and manage emotions, achieve positive goals, show caring and concern for others, establish and maintain positive relationships, and make responsible decisions-are important for success at school and in life. In this article, we summarize key concepts and evidence for systemic SEL. Next, we explain interrelated Theories of Action and resources developed by the Collaborative for Academic, Social, and Emotional Learning (CASEL) to implement and continuously improve systemic SEL in schools, districts, and states. We discuss research on nested, interacting settings and processes involved in systemic SEL at proximal (classrooms, schools, families, and communities) and distal (districts, states, national, and international) ecological levels. We conclude with recommendations for future SEL research, practice, and policy.