Influenza virus is an important human pathogen, frequently causing widespread disease and a significant loss of life. Much has been learned about the structure of the virus, its genetic variation, its mode of gene expression and replication, and its interaction with the host immu nologic system. This knowledge has the potential of leading to ap proaches for the control of influenza virus. In addition, research on influ enza virus has led to important advances in eukaryotic molecular and cellular biology and in immunology. A major focus of this book is the molecular biology of influenza virus....