In Southern Africa, adolescent girls and young women (ages 15-24) make up a disproportionate number of new HIV infections compared to their male peers. In order to become AIDS-free, it is critical to prevent new infections in this key population. This study explores biological and social vulnerabilities young women face in relation to HIV, including engagement in transactional sex, limited education, and amplified effects of transmission. This study stresses the importance of expanding medical and behavioral interventions to meet the prevention needs of adolescent girls and young women.