Despite decades of investment and dramatic progress against HIV, adolescent girls remain at disproportionate risk of infection. Population Council research shows that the best way to protect girls and young women from HIV and other bad outcomes is to reach them early—before they experience irreversible events like HIV infection or unintended childbearing—and with enough health, social, and cognitive assets to make a measurable difference in their lives. This book is a comprehensive review of three programs launched by the Population Council and the Ethiopian government. Two of the programs work to reduce Ethiopian girls’ HIV risk by providing out-of-school adolescent girls in urban slums and married adolescent girls in rural areas with adult female mentors, education on HIV and AIDS and related issues, non-formal education, and links to health services. The third program focuses on husbands, promoting care-giving to wives and children and addressing extramarital partnerships, alcohol abuse, and violence. The Council’s experiences in Ethiopia show that when HIV prevention programs are shaped by evidence and designed for replication and scale-up, they can reach large numbers of the people at greatest risk and increase their ability to avoid infection.