The number of HIV-related deaths each year is falling globally, treatment is becoming more effective and cheaper, yet the rate of new infections is still too high to reach the UN’s goal of less than 500,000 new infections per year by 2020. CGD’s work on the economics of HIV introduced the concept of the AIDS transition—the point in time when the number of people living with the disease begins to fall. Our work also models the effects and implications of policies to reduce new infections and expand treatment.