Additional Study Information: We are working on a new HIV vaccine study that builds on past success and other ongoing studies. This new study is called HVTN 120 and is testing a vaccine for HIV prevention. The Thai Trial has been the only study where the vaccines were partially protective in preventing HIV. We learned a lot from that study, and are now improving on next generation of vaccines. We can only do that with more studies. Sites in Africa are currently testing some of the same vaccine components from the Thai Trial in an important efficacy study. This will also help us improve upon what we know. HVTN 120 tests the same vaccines (ALVAC vaccine and a gp120 protein) as in that large study in Africa and adds another adjuvant, comparing the two adjuvants head to head. Adjuvants help the immune system respond better to vaccines. About 320 people will take part in this study at multiple sites in southern Africa and the United States.We are looking for people who are HIV negative, 18-40 years old and in general good health. We will ask you to complete a brief questionnaire to find out if you are eligible. If you are eligible and decide to participate, you will come to clinic for about 12 visits over 12 months. You will receive an injection of the test vaccine or placebo (dummy shot) in the upper arm at 4 of these visits. If you complete all of the required study procedures, you will be compensated a minimum amount of $900. About 320 people will take part in this study at multiple sites in southern Africa and the United States.