The evolution of influenza is a continuing process involving viral and host factors. The increasing frequency of emergence of the highly pathogenic H5N1, H7N3 and H7N7 influenza viruses and the panzootic spread of H9N2 influenza virus, all of which can be potentially transmitted to humans, are of great concern to both veterinary and human public health officials. The question is how soon the next pandemic will emerge. A convergence of factors, including the population densities of poultry, pigs and humans, are likely factors affecting the evolution of the virus. Highly concentrated poultry and pig farming, in conjunction with traditional live animal or 'wet' markets, provide optimal conditions for increased mutation, reassortment and recombination of influenza viruses. Strategies to reduce the evolution of influenza and the emergence of pandemics include the separation of species, increased biosecurity, the development of new vaccine strategies and better basic knowledge of the virus. More effective co-operation between scientists and veterinary and public health officials is required to achieve these goals.