The necessity to perform forest damage inventories arose with the occurrence of the first forest decline symptoms in large areas. The individual countries, participating in the LAOE, started from the beginning with research work and the establishment of damage assessment methods. These traditional methods are based on terrestrial sample surveys and partly accompanied by the interpretation of aerial photography. The approaches of the inventories, the area coverage and most of all the definition of damage classes varies widely among the countries. Despite of the immense costs and the lacks in providing maps, the biggest deficit is the inability to compare the results of these different damage assessments.