This article considers the history of preparation for flu pandemics since 1976, with a particular focus first on the action of international organizations and then on the French case. Apart from sanitary threats as such, the planning involves a redefinition of 'minimal life'? in complex contemporary societies, taking into account the relations of internal and external interdependence, and simultaneously shaping risks and security measures to reduce them. The abundant criticism of public action taken to deal with the 2009 pandemic has not resulted in preparation being scrapped. Instead, it has led to a more in-depth approach to preparation, taking into account the endogenous risks in planning (closure of hypotheses, irreversibility) in order to produce ever more security.