The contribution of bovine viral diarrhea viruses (BVDV) to the development of bovine respiratory disease is the sum of several different factors. These factors include the contribution of acute uncomplicated BVDV infections, the high incidence of respiratory disease in animals persistently infected with BVDV, the immunosuppression that accompanies acute BVDV infections and predisposes animals to secondary infections, and the synergy resulting in increased virulence occurring in coinfections of BVDV with other pathogens. Immunosuppression, which is associated with infection with all BVDV, may have the greatest impact of these factors. Control of BVDV infections rests on reducing exposure by removing BVDV persistently infected animals, increasing herd resistance by vaccination, and instituting biocontrol methods that limit the opportunity for introduction of BVDV into herds and management units.