In the history of influenza there are many references, notes and comments about influenza epizootics occurring among various non-human animals, sometimes co-inciding with epidemics of influenza in human beings. That the first influenza viruses were recovered from non-human animals is not so surprising, given the current knowledge of the distribution of influenza among animals. Influenza viruses are found in a wide variety of mammalian and avian species. In some species the disease that occurs as a result of the infection mimics the influenza disease of human beings, in other species there are no signs of disease, and in others there is disease specific to a species. It is clear that influenza viruses have a significant impact on the health of several animal species. In recent times it has also become clear that many species of animals are inextricably entwined in the puzzle of influenza viruses and human influenza. Our knowledge in animals has provided both questions and answers about the influenza viruses and their diseases. Certainly our understanding of human influenza has been advanced because of the animals in the influenza world.