Surveillance is the "continuous and systematic process of collecting, compiling, and analyzing health data, as well as disseminating that data to all those who contributed to its collection and to all those who need to be informed in order to take action." Directly linked to action and decision-making, surveillance activities focus primarily on health issues that can be treated, prevented, or addressed through public health measures. The objectives of surveillance are to monitor trends and characteristics of the disease in question; to evaluate policies and strategies for the control and prevention of infectious diseases; and to provide early warning through the detection of emerging infectious diseases and the onset of epidemics. The information generated in this way makes it possible to prioritize actions and to refine or even define control and prevention objectives. Infectious disease surveillance relies on numerous partners and stakeholders who form a national public health network in which clinicians and biologists are on the front lines. The French infectious disease surveillance system is based on mandatory reporting, national reference centers, networks of volunteer professionals, and repeated surveys. These systems are coordinated by the Institute for Public Health Surveillance, whose mission is to monitor the health status of the population, alert public authorities to public health threats, and study the determinants of changes in health trends.