Bluetongue viruses (BTV) cause diseases that have serious economic consequences in ruminants (sheep, cattle) in many parts of the world. The incidence of bluetongue disease affects the international movement of animals and germ plasm. Although the etiological agent of the disease was isolated in 1900 and preliminary biochemical characterizations were pub­ lished as early as in 1969, most of the current understanding of the molecular biology, biochemistry, and genetics of BTV has evolved only recently. Triggered by the modern techniques of molecular biology, genetics, and immunology, BTV research has experienced an information explosion in the past 10 years. However, much of this information is scattered throughout an extensive literature. It is therefore an appropriate time to meld this together into a reference book. This book includes compre­ hensive information on BTV research provided in articles contributed by researchers from around the world. It covers what is known about the molecular structure of the virus and the current understanding of its biology, evolution, and relationships with its invertebrate and vertebrate hosts (infection, immunity, and pathogenicity).