New viral diseases are emerging continuously. Viruses adapt to new environments at astounding rates. Genetic variability of viruses jeopardizes vaccine efficacy. For many viruses mutants resistant to antiviral agents or host immune responses arise readily, for example, with HIV and influenza.These variations are all of utmost importance for human and animal health as they have prevented us from controlling these epidemic pathogens. This book focuses on the mechanisms that viruses use to evolve, survive and cause disease in their hosts. Covering human, animal, plant and bacterial viruses, it provides both the basic foundations for the evolutionary dynamics of viruses and specific examples of emerging diseases explained by the evolutionary flexibility of the viral agents that circulate in a continuously changing earth environment.* NEW to this edition - chapters on the molecular basis of copying fidelity of viral polymerases, methods to establish phylogenetic relationships among viruses, and the mechanisms of cellular RNA interference and editing functions as they affect virus evolution.* UNIQUE - combines theoretical concepts in evolution with detailed analyses of the evolution of important virus groups.* Bacterial, plant, animal and human viruses are compared regarding their interaction with their hosts.