Infectious diseases are responsible for significant morbidity and mortality in France every year. Surveillance of these diseases must provide information to improve our understanding of their epidemiology (temporal and spatial dynamics, changes in clinical and microbiological characteristics), in order to implement appropriate control and prevention measures, as well as to detect the occurrence of any new or abnormal phenomenon (epidemic, emergence of a new syndrome, resurgence of a disease, etc.). In France, this surveillance currently relies on a partnership among multiple public and private health stakeholders (physicians, biologists, networks, laboratories, etc.). The activities of these various partners are largely coordinated by the Institute for Public Health Surveillance, whose mission is to continuously monitor the health status of the French population and alert public authorities to public health threats. This article outlines the objectives and procedures for infectious disease surveillance in France by describing the main systems and stakeholders. The concept of an alert is defined, and the various possible alert scenarios are described using recent examples. In the rapidly evolving context of the epidemiological trends of infectious diseases, it is essential to have appropriate and responsive tools to identify infectious threats to public health as early as possible. Applied research is also necessary to better understand the origins of these phenomena.