The cat has been living in close association with human for at least 3500 years and currently, the cat is the world’s most popular household pet. Feline influenza is an infectious disease that affects the upper respiratory tract and clinical signs usually appear within 1 to 3 days. Feline influenza virus (influenza type A) is the virus under the family Orthomyxoviridae (a group of RNA viruses). Influenza virus A infects humans, other mammals, and birds, and causes all flu pandemics. Its ability to cross the species barrier without prior adaptation and to infect many mammal species including cat, has raised concerns about a new influenza pandemic. Influenza type A has been long absent from the list of infectious diseases considered as possibilities in dogs and cats. With the discovery that avian influenza H5N1 can infect cats and dogs, small animal veterinarians have an important role to play in detection of influenza virus strains that may become zoonotic. In cats, the clinical signs are fever, decreased activity, protrusion of the nictitating membrane, conjunctivitis and laboured breathing. This book illustrates the introduction, diagnosis and prevalence of influenza in cats.