This book gives a synthesis of current knowledge on ret- rovirology. Each chapter deals with a different step in the virus life cycle, detailing the molecular aspects of virus replication. The comparison of different retroviruses exemplifies variations. Specific topics include the evolution of retrovirus genomes, integration of the provirus, viral DNA transcriptional and translational control of viral gene expression, processing of viral proteins, and packaging of virion RNA. Data on HIV and HTLV-1 are covered as well as research on animal retrovirus sys- tems.