Canine influenza, as a recognized clinical entity in dogs, has a relatively brief history. The presence of specific subtypes of influenza virus capable of being transmitted from dog to dog is at present geographically limited to the United States and Korea. As surveillance intensifies to meet the concerns of the human population on pandemic influenza viruses, more cases of influenza virus in dogs are certain to be detected. Each infection offers an opportunity for a unique variant to emerge and continue the evolution of influenza virus as a species-crossing pathogen.