This first brief in our series focuses on how afterschool programs contribute to the development of social and emotional competencies in young people. In practice, we see how high-quality programs can help participants learn, grow, and develop. But what does the research say? How can we prove it? We chose to focus our first brief on this important topic because there has been a growing recognition that afterschool programs can and do facilitate the social and emotional development of young people. Despite the recent attention this topic has received, efforts to define and measure social and emotional competencies in afterschool settings are still emerging. This brief provides an overview of work done to date both in afterschool and school-based settings to define social and emotional learning, shares recent research on how afterschool programs contribute to the development of these competencies, and, finally, offers some next step recommendations to both practitioners and researchers. (author abstract)