Raltegravir is the first approved human immunodeficiency virus type 1 (HIV-1) integrase inhibitor; it targets the strand transfer step of HIV-1 integration. Clinical trials have demonstrated that raltegravir-containing regimens have potent antiretroviral activity and are well tolerated in HIV-1-infected individuals. In antiretroviral treatment-experienced persons with drug-resistant HIV infection, raltegravir-containing treatment with an optimized background regimen was superior to an optimized background regimen alone. In treatment-naive persons, raltegravir was not inferior to efavirenz when the drugs were administered with tenofovir and lamivudine or emtricitabine. Raltegravir is metabolized by glucuronidation, not hepatically; thus, the potential for drug-drug interactions is decreased. Drug resistance, conferred by substitutions in the gene coding for the HIV-1 integrase enzyme, develops relatively frequently after virologic failure. As an antiretroviral drug with a novel mechanism of action, raltegravir is an important advancement in HIV-1 treatment options.