Strategic planning of forest resources in Europe requires reliable information on the status and trend of forest condition. National Forest Inventories (NFIs) and Forest Condition Monitoring (FCM) networks are primary sources of data for large area assessments of forest resources. This contribution seeks to outline a statistical perspective for the construction of a European forest monitoring system, able to provide statistically sound estimates of forest condition (defoliation) parameters and of their changes over time. Monitoring objectives, parameters of interest, and accuracy indexes are presented, under the assumption that a common definition for forests is adopted by European countries. The proposed estimators are of two types: (i) based solely on information acquired from FCM and (ii) derived from integration of FCM and NFIs.