This study sheds light on the mechanisms producing the official data used by humanitarian aid decision makers. It views Early Warning Systems (EWS) as tools that facilitate consensus between the decision-makers involved in the allocation of food aid, enabling them to reach institutional agreements. This argument is strengthened by a socio-theoretical analysis and by ethnographic observation of experts' practice in Ethiopia (2002-2004), whose results of food aid evaluations appear as a combination of empirical and political factors.