The burden of seasonal influenza in terms of morbidity and mortality, combined with the threat of a pandemic, makes influenza a major public health issue. The objectives of influenza surveillance are to estimate the burden of the disease, identify any abnormal situations in order to best adapt control measures, and evaluate the actions taken. In France, this surveillance is coordinated by the French Institute for Public Health Surveillance (InVS) and has been significantly strengthened since 2003 as part of preparations to combat an influenza pandemic. The lack of specificity in the clinical signs of the disease, the frequent and unpredictable mutations of the influenza virus, and the varying patterns of healthcare utilization make this surveillance complex and necessitate the implementation of several systems with complementary objectives. (R.A.)