Influenza is a disease with global impact that causes enormous morbidity and mortality on an annual basis. It primarily infects the respiratory tract and causes a broad range of illness ranging from symptomless infection to fulminant primary viral and secondary bacterial pneumonia. The severity of infection depends on both the virus strain and a number of host factors, primarily age and the presence of comorbid conditions such as cardiopulmonary disease. The mortality and utilization of healthcare resources associated with influenza is concentrated in the elderly and those with coexisting disease such as chronic obstructive pulmonary disease (COPD). Increasing use of vaccination and the development of new antiviral drugs hold out hope that the burden of disease associated with influenza can be reduced. However the constant emergence of new influenza strains and the current risk of avian influenza pandemic serve as warnings that influenza will remain a serious pathogen for the foreseeable future.