Since the discovery of HIV, scientists have made major inroads in understanding modes of transmission, infectivity, and pathogenicity. Knowledge about the characteristics and behavior of this human retrovirus and its complex mechanisms of immunopathogenesis has helped to develop targeted therapeutic interventions and vaccine strategies. Sophisticated techniques have been and are being developed to diagnose infection, to monitor immune decline, to monitor response to therapy and disease progression, and to accurately detect and diagnose opportunistic diseases. As the demographics of HIV infection evolve, both in the United States and around the world, it is clear that all healthcare professionals in all practice settings will be involved to some extent with HIV infection. To be effective and provide compassionate care, adequate and up-to-date information about transmission, prevention, diagnosis, treatment, and care of HIV-infected individuals should be obtained by all healthcare professionals.