The number of people infected by HIV-1 worldwide continues to increase. However, antiretroviral therapy is largely unavailable in low- and middle- income countries where risk of infection is very high. The development of a safe and effective vaccine to prevent HIV infection is urgently needed. This study will evaluate the effectiveness, safety, and immunogenicity of an experimental multiclade HIV vaccine, VRC-HIVDNA016-00-VP, followed by an adenovirus-vectored vaccine boost, VRC-HIVADV014-00-VP, in HIV uninfected adults. Both vaccines code for proteins from HIV subtypes A, B, and C, which together represent 75% to 85% of new HIV infections in the world. Adenoviral type 5-based vaccines have improved induction of HIV-specific CD8 cytotoxic T-lymphocyte cell responses, which correlate with lower HIV burden (viral load) and slower disease progression in primates and in HIV-1 infected people whose disease does not progress over the long term. The purpose of this study is to determine the safety and effectiveness of and immune response to a series of multiclade DNA vaccine injections followed by a booster injection of a multiclade adenovirus vaccine against HIV-1 infection in healthy adults at risk for HIV infection in North and South America, the Caribbean, and Africa.