Social and emotional learning (SEL) is the process of integrating cognition, emotion, and behavior in our lives. In school settings, it involves systemic practices to incorporate SEL into leading, teaching, learning such that adults and children build self- and social awareness, learn to manage their own and other's emotions and behavior, make responsible decisions, and build positive relationships. Here, we describe RULER, a systemic evidence-based approach to SEL, including its Theory of Change, and key theories that are foundational to the approach. RULER's implementation model also is described, which involves training for school leaders, educators, and staff; integrating SEL into the curriculum across grade levels; infusing SEL into schoolwide practices and policies; and engaging families and the broader community. RULER's current and expected outcomes for children and adults are reviewed, including both proximal (e.g., more developed emotion skills and enhanced classroom climate) and distal (e.g., reduced teacher stress and burnout and greater academic performance) outcomes. RULER's future directions also are discussed.