In the past three years, expanding access to antiretroviral therapy (ART) for HIV/AIDS has become a global objective and a national priority for many countries in sub-Saharan Africa. Large-scale treatment programs have been launched in countries spanning the continent from Lesotho to Ghana, paid for by domestic funds mobilized by African governments and by international donor contributions. While these funds, which reach into the billions of dollars, will pay for ART for many thousands of HIV-positive Africans, there is almost no chance that African countries will have the human, infrastructural, or financial resources to treat everyone who is in need. National plans for treatment rollout typically call for a specific number of patients to initiate therapy within the first one or two years of the program. Though the target patient numbers are extremely ambitious—often requiring a 10-fold expansion of services over a two-year period—they still represent a minority of those who are eligible for antiretrovirals on even the most conservative medical grounds. Table 1 indicates the demand for and supply of ART in several African countries and globally, based on starting ART at a CD4 count of 200 cells/μl or an AIDS-defining illness.