The devastating consequences of AIDS pandemic will probably only be controlled when a vaccine is developed that is safe, effective, affordable, and simple enough to permit implementation in developing countries where the impact of AIDS is most severe. However, the major obstacle for the control of the spread of AIDS lies in the diversity of HIV and its enormous evolutionary potential. Numerous HIV forms contribute to the AIDS pandemic. Two viral types (HIV-1 and HIV-2), numerous groups (M, N and O for HIV-1 and A through H for HIV-2) and numerous subtypes, sub-subtypes and circulating recombinant forms (CRF) have emerged during the last 50 years. At least nine different genetic HIV-1 subtypes and over 20 CRFs were defined within group M, which accounts for the majority of cases in the AIDS pandemic. Even though HIV-1 subtype C and A predominate globally, the other viral forms co-circulate all over the world and may have a major impact for the strategies of pandemic control. Here we discuss the distribution of these divergent viral forms worldwide and the potential consequences of such a tremendous viral diversity for diagnostic, monitoring, treatment and the development of an effective vaccine.