Infectious bronchitis (IB) has become one of the major respiratory diseases in the poultry industry worldwide since its first report in 1931. Its causative agent is infectious bronchitis virus (IBV), an avian coronavirus. The IBV mutates, and its genome combines frequently under selection pressure, driving changes in tissue tropism, pathogenicity, and antigenicity. Contagious IBV spreads horizontally and infects broilers, breeders, and layers of all ages, with high morbidity and mortality often occurring in chicks. Clinical signs such as respiratory distress, nephritis, proventriculitis, enteritis, “false layers” syndrome, decreased egg production, and a reduced growth rate are associated with IBV infection. Rapid tools and methods for detecting IBV are currently available. New IBV genotypes and serotypes are emerging: some are confined to certain areas, whereas others are spreading across regions. Different types of strains may be present on farms at the same time, and vaccine failures frequently occur. Therefore, proper vaccine administration, real-time surveillance, and strict biosecurity measures are the keys to effective control strategies. This chapter discusses the history, etiology, epidemiology, clinical signs, pathology, diagnosis, immunity, prevention, and control of IBV.