Fowl adenoviruses (FAdVs) belong to the group I avian adenovirus that includes conventional avian adenoviruses sharing a common group antigen. FAdVs have been classified by their serological relationships. According to the American classification, 12 fowl serotypes (FAdV1 to FAdV12) have been recognized to date. These12 FAdV serotypes have been grouped in five species (Fowl adenovirus A to E) by the International Committee on taxonomy of viruses. Such viruses are regularly isolated from chickens but thepathogenic role of most of the FAdVs is still questionable. The widespread occurrence of antibodies and the isolation of FAdVs from clinically healthy chicks argue against a primary role of FAdVs in a specific poultry disease. However, some FAdVs were shown to be involved in the aetiology of respiratory disease, inclusion body hepatitis and infectious hydropericardium, Angara disease or hepatitis/hydropericardium syndrome.