Avian influenza (AI) is an infectious viral disease mainly affecting birds. It is often causing no apparent signs of illness. AI viruses can sometimes spread to domestic poultry and cause significant outbreaks of serious disease. The aim of this handbook is to provide the most updated information (aetiology, epidemiology, clinical signs, diagnosis, control...) of these viruses with a practical and visual approach. The handbook has been written by prestigious and renowned experts with a wide experience in this field. Numerous graphic resources have been included to complement the information provided and make the contents more understandable and accessible to readers.