Avian infectious bronchitis (IB) is caused by the Gammacoronavirus infectious bronchitis virus (IBV). The virus causes infections mainly in chickens and is a significant pathogen of commercial meat and egg type birds. IB is an acute, contagious disease characterised primarily by respiratory signs in growing chickens. The disease is transmitted by the air-borne route, direct chicken-to-chicken contact and indirectly through mechanical spread (contaminated poultry equipment or egg-packing materials, manure used as fertiliser, farm visits, etc.). IB occurs world-wide and assumes a variety of clinical forms, the principal one being respiratory disease that develops after infection of the respiratory tract tissues following inhalation or ingestion. Infection of the oviduct at a very young age can lead to permanent damage and, in hens, can lead to cessation of egg-laying or production of thin-walled and misshapen shells with loss of shell pigmentation. IB can be nephropathogenic causing acute nephritis, urolithiasis and mortality, especially in young birds. After apparent recovery, chronic nephritis can produce death at a later time. Both live attenuated and oil emulsion inactivated vaccines are available. Vaccine and field strains of IBV may persist in the caecal tonsils of the intestinal tract and be excreted in faeces for weeks or longer in clinically normal chickens. There have been no reports of human infection with IBV.