Social and Emotional Learning (SEL) refers to the process through which individuals learn and apply social, emotional, behavioral, and character skills required to succeed in schooling, the workplace, relationships, and citizenship. In public discussion of SEL, not everyone can quite agree on what it is. To some, it involves a set of tools for learning, while others see it as a way of promoting resilience in the face of both normative and traumatic stresses. Others see it as a system of values, virtues, habits, and personality or character traits. Still others focus on the importance of neurocognitive skills such as working memory or cognitive flexibility. This lack of consistency does not mean, that SEL is "soft," immeasurable, irrelevant, or faddish. According to the Aspen Institute's National Commission on Social, Emotional, and Academic Development, "It means that social and emotional development is multifaceted and is integral to academics--to how school happens, and to how learning takes place." Generally, SEL skills can be grouped into three interconnected domains: (1) Cognitive regulation skills; (2) Emotional competencies; (3) Social and interpersonal skills. Interest in SEL is high among education leaders, practitioners, and policymakers. There is clear evidence that promoting SEL via high-quality programs, systems, and strategies in both school and out-of-school settings can be effective. There are multiple ways that schools and districts approach SEL. Most common are school-based prevention and intervention programs, typically comprehensive, scripted curricula with sequenced lessons and explicit instruction in SEL skills--some emphasizing conflict resolution, others focused on empathy, and others targeting a range of skills and competencies. In many settings, it can be difficult to implement comprehensive SEL programs, which often offer teachers and schools inadequate flexibility or adaptability. This article details some guides state policymakers could use to shape and decide which statewide efforts to employ. The guidelines provided are organized around four actions: (1) conducting a needs assessment; (2) alignment of approaches; (3) focus on adults; and (4) development and communication of a plan.