First, we study the complex HIV-1 population that exists within a person. We use this complexity to ask questions about viral evolution, transmission, compartmentalization, and pathogenesis. Second, we are exploring the impact of drug resistance on viral fitness and identifying new drug targets in the viral protein processing pathway. Third, we participate in a collaborative effort to develop an HIV-1 vaccine. Fourth, we are using mutagenesis to determine the role of RNA secondary structure in viral replication.