Influenza is a serious infectious disease caused by different influenza viruses that can mutate to form new strains. Some of these strains give rise to epidemics or pandemics, infecting millions worldwide each year. Because evolutionary changes in these viruses are difficult to predict and our understanding of their pathogenic effects is incomplete, the development of effective vaccines and therapeutics for influenza remains challenging. Written and edited by experts in the field, this collection from Cold Spring Harbor Perspectives in Medicine reviews cutting-edge research on the viruses that cause influenza, the molecular mechanisms of infection, the epidemiology of these viruses in humans and animals, and current strategies for designing vaccines and antivirals. Contributors discuss all aspects of the molecular virology of influenza--the viral and host factors involved in the attachment and entry into host cells, the transcription and replication of viral genomes, and virus assembly and budding. The various factors and conditions that determine susceptibility to influenza infection and disease severity are also covered, as is our current understanding of the ecology and evolution of influenza viruses, the various subtypes, and their transmission and epidemiology in humans, birds, swine, bats, and other animals. In addition, the authors examine the human immune response to influenza infection, insights gained from animal models, and technological advances in the design and delivery of vaccines and antivirals. This volume is therefore an essential reference for all virologists, clinical and laboratory investigators, and physicians interested in reducing the global public health burden of influenza.