RNA viruses are a major threat to human health and well-being. They also provide a fascinating window into cell biology and immunology, since they interact intimately with their hosts at both a cellular and systemic levels. The constant interplay between viruses trying to establish infection and the host trying to control them present an ideal system to study evolution in action. The Andino lab is interested in understanding these diverse but interconnected aspects of RNA virus biology. First, they examine at a molecular level the mechanisms of virus replication, such as virus protein synthesis, genome replication, and viral particle formation and their interplay with cellular processes. Secondly, they study the host strategies that control virus infection, including innate immune responses, such as RNAi and the mechanisms that the virus has evolved to suppress the host antiviral responses. Lastly, they are developing novel approaches to study virus population dynamics and evolution at the molecular and genomic level, and the consequences of these evolutionary strategies for viral pathogenesis and the epidemiology of viral diseases. Understanding the mechanisms of virus evolution is essential to both development of antiviral therapies and vaccine design.