This book is the proceedings of the VIII International Symposium on Nidoviruses (Coronaviruses and Arteriviruses), held May 20-25, 2000, in Philadelphia, Pennsylvania, USA. It summarizes current knowledge concerning this group of viruses and details the genomic structure of the viruses, the mechanism of their entry into cells, their mechanism of replication, RNA synthesis, and particle assembly within cells. The book also describes the epidemiology of these viruses, their pathogenesis, and the role of the immune system in interacting with these viruses.