Reactive monitoring is the reporting by the World Heritage Centre, other sectors of UNESCO and the advisory bodies to the Committee on the state of conservation of specific World Heritage properties that are under threat.

To this end, the States Parties shall submit to the Committee through the World Heritage Centre, specific reports and impact studies each time exceptional circumstances occur or work is undertaken which may have an effect on the state of conservation of the property.

Reactive monitoring is foreseen in the procedures for the eventual deletion of properties from the World Heritage List as set out in paragraphs 48-56 of the Operational Guidelines. It is also foreseen in reference to properties inscribed, or to be inscribed, on the List of World Heritage in Danger as set out in paragraphs 86-93.