AIDS (acquired immunodeficiency syndrome) is the most deadly epidemic of modern times. Since HIV (human immunodeficiency virus), the virus that causes AIDS, was first identified in the United States in 1981, nearly 1 million Americans have been diagnosed with AIDS and 530,756 have died. Forty million people are living with HIV worldwide. Although AIDS is still a fatal disease, new drug therapies have greatly slowed the course of disease progression and enhanced quality of life for persons living with HIV. Nevertheless, monumental disparities persist within the United States and between the developed and developing worlds in this two-tiered epidemic.