Purpose of review: Respiratory syncytial virus (RSV) infection is the leading cause of bronchiolitis and hospitalization in young infants and causes 100 000–200 000 deaths annually. There is still no licensed vaccine against RSV infection and the therapeutic options are mainly supportive. Despite almost six decades of research, important knowledge gaps remain with respect to the characterization of immune mechanisms responsible for protection and pathogenesis, as well as to the identification of risk factors that predict the severity of infection. Recent findings: Observations made in mouse models and young children suggest that the early innate immune response plays a major role in the pathogenesis of bronchiolitis due to RSV infection. Recent studies have improved our understanding...