In 2002, a new coronavirus (CoV) emerged in the People's Republic of China, associated with a severe acute respiratory syndrome (SARS) and mortality in humans. The epidemic rapidly spread throughout the world before being contained in 2003, although sporadic cases occurred thereafter in Asia. The virus is thought to be of zoonotic origin from a wild animal reservoir (Himalayan palm civets [Paguma larvata] are suspected), but the definitive host is unknown. There is concern about possible transmission of SARS CoV to rodents or domestic cats (as proven experimentally) with perpetuation of the disease in these species. In livestock and poultry, CoVs are recognised causes of enteric and respiratory infections that are often fatal in young animals. Although the emergence of SARS surprised the medical community, veterinary coronavirologists had previously isolated CoVs from wildlife and documented their interspecies transmission to livestock. Furthermore, scientists were aware of compelling evidence pointing to the emergence of new CoV strains and the mutation of existing strains resulting in new disease syndromes in animals, but the evolution and disease impact of CoVs was not widely appreciated before SARS. This review focuses on the comparative pathogenesis of CoV infections, including the factors that accentuate CoV respiratory disease, with emphasis on livestock and poultry. The goal is to provide insights into CoV transmission and disease mechanisms that could potentially be applicable to SARS, highlighting the contributions of veterinary scientists to this area of study. Such examples illustrate the need for communication and collaboration between the veterinary and medical communities to understand and control emerging zoonotic diseases of the 21st Century.