The medical, social, and economic impact of the human immunodeficiency virus (HIV) epidemic has underscored the need to quickly develop effective control strategies. Vigorous efforts to develop a vaccine and therapeutic agents have not yet succeeded in containing the spread of the virus. Studies of persons who remain uninfected despite extensive exposure to HIV continue to provide valuable information on mechanisms of natural protection, which can then be applied to vaccine design. Natural resistance to infection has been studied in multiple high-risk cohorts, with resistance attributed to a combination of innate, genetic, and acquired immune system-mediated mechanisms. The relative contributions of these factors to natural resistance to HIV-1 infection and possible ways in which they can be applied to vaccine design are discussed.