This white paper is a collaboration of the Claremont Evaluation Center, Child Trends, and L.A.’s Best (a large afterschool program in Los Angeles) that sought to address the knowledge gap related to how afterschool practices can support positive youth development (PYD). The authors conducted a research review to show how afterschool programs can build protective and promotive factors associated with supporting PYD. The paper examines which outcomes are important to develop during childhood and adolescence, which protective and promotive factors support positive youth outcomes, and which evidence-informed practices show promise for afterschool programs. (author abstract modified)