Out-of-School Time (OST) programs play a crucial role in child and youth development, serving as a bridge between school, home, and the community. They offer structured environments where young people can engage in meaningful activities, build relationships, and develop essential life skills. OST programs foster personal growth, academic support, career exploration, and social-emotional development. Since the release of the National Academies' 2002 foundational report, Community Programs for Youth Development (the "Blue Book"), OST programs have evolved significantly. The Future of Youth Development examines the effectiveness of OST programs and identifies access and quality improvements. This book describes the array of OST activities; evaluates their effectiveness in promoting learning, development, and well-being; outlines improvements to existing policies and regulations to increase program access and quality; and lays out a research agenda that would strengthen the OST evidence base. The conclusions and recommendations of The Future of Youth Development will guide and support a sustainable OST system that meets the evolving needs of young people across the country.