Solid evidence on the links between preventing adolescent childbearing and alleviating poverty can motivate policymakers and donors to invest in reproductive health and family planning programs for youth. Research that documents the clear cause-and-effect relationship between program interventions and outcomes, such as better health and delayed childbearing among teens, can guide decisions about investments in research or programs. This report examines the evidence for investing in adolescent reproductive health and family planning programs from the perspective of making an evidence-based argument to guide the investment or spending decisions of public or private organizations. Key steps in developing such an argument—a business case—include the consequences of relevant trends, evidence on the potential of particular actions or interventions to change the status quo, and the costs associated with different actions. This report highlights new research from the Population and Poverty (PopPov) Research Initiative that bolsters the case for these investments and identifies knowledge gaps where research is still needed.