Once every six years, starting in 1999, a periodic report is drawn up for each World Heritage site. The reports are compiled by region according to a fixed order. From June 2003 up to and including July 2006 the European and North American World Heritage reports are due on the sites inscribed up to 1998. The periodic reports are drawn up on the basis of questionnaires sent out by the World Heritage Committee. ICOMOS and IUCN make recommendations based on the outcome of these reports.

The periodic reports give an account of the legal, administrative and other measures that have been taken to meet the obligations ensuing from the World Heritage Convention. The reports are also aimed at determining the state of preservation of each area or object on the World Heritage List. Monitoring means systematically analysing the state of affairs.

Periodic reporting or monitoring has four main objectives:
1. To provide an assessment of the application of the World Heritage Convention by the State Party
2. To provide an assessment as to whether the World Heritage values of the properties inscribed on the World Heritage List are being maintained over time
3. To provide up-dated information about the World Heritage properties to record the changing circumstances and state of conservation of the properties,
4. To provide a mechanism for regional cooperation and exchange of information and experiences between States Parties concerning the implementation of the Convention and World Heritage conservation.