Technical Abstract: Avian influenza virus (AIV) is type A influenza, which is an orthomyxovirus. The ability of the virus to evolve and mutate is a major factor in how the virus behaves biologically as it can adapt to different hosts and ecological niches very rapidly. The natural host species for AIV is waterfowl and shorebirds, although the virus can infect numerous avian and mammalian hosts in a strain dependent manner. Importantly, gallinaceous poultry (chickens, turkey and quail) are not natural hosts for the virus. Introduction of AIV into poultry results in genetic changes in the virus. These genetic changes may be used to loosely determine how long an isolate has been circulating in a non-natural host species. The basic biology of AIV in poultry is discussed.