Viral pathogenesis and immunity encompass all aspects of infection of animal hosts, which include the sequence of events from entry to shedding, the clearance or persistence of the virus, the immune response of the host and the subsequent occurrence of disease. In recent years, emerging viral diseases pose serious threats to humans and animals, and they have incurred tremendous financial and societal costs for decades. In addition to demographic, ecological, and anthropogenic factors, virological and host determinants play critical roles in the emerging and evolving of new viral diseases. Understanding these virological and host determinant factors will help explain how certain viruses such as H5N1, H7N9 avian influenza cross species barriers to infect humans, and how SARS-like coronavirus develops evolving changes in the pathogenesis and evasion of the host immune defense. This course will explore, at the molecular level, the mechanisms behind animal viruses infection, and animal hosts’ immune responses to the sophisticated invaders.