Public health surveillance is the “process of systematically, organizedly, and continuously collecting health data, as well as analyzing, interpreting, and disseminating it to aid in decision-making and evaluation.” The natural link between surveillance and public health action necessarily implies that surveillance systems should focus primarily on health issues that carry sufficient weight in public health (frequency, severity, mortality, social impact, etc.), significant potential for spread (particularly epidemic risk), and that they are preventable (availability of treatment, preventive measures, or, more broadly, effective and feasible public health interventions, particularly through public initiatives). The objectives of public health surveillance are to assess the magnitude of a health phenomenon, characterize the affected population, identify trends, contribute to the evaluation of health programs, detect health threats to implement early control measures, and formulate research hypotheses. Surveillance systems can be mandatory or voluntary, comprehensive or based on samples from data sources, specific or nonspecific (also called syndromic), passive or active, or based on continuous and periodic data collection. In France, public health surveillance is part of the activities of the Institut de Veille Sanitaire, which coordinates a group of partners within the framework of a national public health network. The regionalization of surveillance systems has become a major objective for the coming years. (R.A.)