Abstract: Forest condition has been observed in Europe for 16 years through one of the world’s largest biomonitoring networks, mainly aiming at the monitoring of air pollution effects. The crown condition of the forests in Europe deteriorated considerably during the first decade of monitoring. After some recuperation in the mid-1990s the deterioration resumed. In 2001 more than 20 % of the sample trees were rated as damaged. The most important causes of this damage include extreme weather conditions, insect and fungi attack and air pollution. Depositions of nitrogen, acidity and heavy metals exceed critical loads over a large proportion of the Intensive Monitoring Plots, indicating enhanced risks for leaching of aluminium and base cations, tree root damage, crown damage by drought, frost and pests and changes in the plant diversity of ground vegetation. Plant diversity is mainly determined by actual soil condition, specifically acidity, as well as nitrogen deposition, temperature, precipitation and tree species.