Event-based surveillance (EBS) is defined as the organized collection, monitoring, assessment and interpretation of mainly unstructured ad hoc information regarding health events or risks, which may represent an acute risk to health. Both indicator-based and event-based surveillance components serve the early warning and response (EWAR) function of the public health surveillance system. The Framework for Event-based Surveillance offers guidance to public health practitioners seeking to implement EBS at each administrative level in their countries.