Timely collection and exchange of information on influenza activity is of utmost importance when it comes to reducing the burden of influenza worldwide. National and international networks for the clinical and virological surveillance of influenza have therefore been established everywhere. The WHO Global Influenza Surveillance Network comprises 4 WHO Collaborating Centres (London, Tokyo, Atlanta and Melbourne) and 122 institutions in 94 countries, which are recognized by WHO as WHO National Influenza Centres (NICs). These NICs collect specimens in their country, and perform primary virus isolation and preliminary antigenic characterization. They ship newly isolated strains to WHO Collaborating Centres for high-level antigenic and genetic analysis, the result of which forms the basis for WHO recommendations on the composition of influenza vaccine for the Northern and Southern Hemisphere each year. The National Influenza Centres themselves receive their information from a network of sentinel general practitioners and hospitals. Such a sentinel network usually represents 1-5% of physicians working in a country or region. The sentinel physicians are asked to take nose and/or throat swabs from patients with ILI and to send these to their reference lab for testing. Information about the conditions for taking part in the sentinel surveillance system in your country can be obtained from your National Influenza Centre – a list of these Centres can be found on the WHO website. In the EU, the European Influenza Surveillance Scheme organizes influenza surveillance on a supranational level.