Infection with the human immunodeficiency virus (HIV) continues to affect millions of people worldwide. Preventive measures have done little to slow the transmission of the virus. Discovery of an effective vaccine to prevent HIV could have a tremendous impact on this global pandemic. However, the complex interactions between HIV and the host immune system have limited the progress in vaccine development. Traditional vaccination strategies have shown little promise. Currently, subunit vaccines, DNA vaccines, recombinant vector vaccines, and prime-boost strategies are being evaluated in clinical trials. Although many breakthroughs have been made in HIV vaccine research, only three candidate HIV vaccines have been studied in phase III clinical trials. The current strategies being investigated in the development of preventive HIV vaccines are reviewed.