Adolescents (ages 10–19) and youth (ages 15–24) bear a disproportionate share of the HIV burden, especially in sub-Saharan Africa. However, little is known about what projects are doing to make their interventions adolescent- and youth-friendly and what interventions are effective for changing HIV-related outcomes for these age groups. Program managers and policymakers have little rigorous evidence on how best to invest resources to achieve 90-90-90 targets among adolescents and young people. Recognizing this evidence gap, MEASURE Evaluation—funded by the U.S. Agency for International Development (USAID)—reviewed the evidence on adolescent- and youth-friendly HIV services as a contribution to the goal of an AIDS-free generation that the U.S. President’s Emergency Plan for AIDS Relief (PEPFAR) is pursuing. This review had three objectives: (1) document knowledge of what is working and what is not working in terms of delivering adolescent- and youth-friendly HIV services, and why strategies and program activities work or do not work; (2) identify useful lessons learned about key elements of successful adolescent- and youth-friendly HIV services; and (3) promote the use and adaptation of best practices for adolescent- and youth-friendly HIV services in order to improve the quality of HIV services delivered to young people and to attract adolescents and youth to retain them in those services.