Avian influenza (AI) is caused by Influenza A viruses, and are single stranded, segmented RNA viruses of the family Orthomyxoviridae. Influenza A viruses continue to pose a major threat to the poultry industry and to the public. Wild aquatic birds are considered the primary hosts of influenza A, in which the virus is enzootic. In these birds, influenza viruses usually replicate in the intestinal tract, cause disease, and spread by fecal contamination of the water habitat. This book discusses the epidemiology, global patters, and clinical management of Avian Influenza. It also examines the symptoms, treatment and clinical outcomes of Severe Acute Respiratory Syndrome (SARS), which is a highly contagious respiratory disease caused by a SARS coronavirus.