The purpose of this Funding Opportunity Announcement (FOA) is to invite grant applications to support research in two key emerging areas in HIV neuropathogenesis research. One key area relates to understanding the mechanisms that regulate the changing phenotype of HIV-associated central nervous system (CNS) disease in the era of highly active anti-retroviral therapy (HAART). A second area of emphasis are studies of viral (clade diversity) and host genetic mechanisms regulating HIV neuropathogenesis from a world wide perspective. Both basic and clinical research applications are encouraged. Multidisciplinary research teams and collaborative alliances are encouraged, but not required.