Book excerpt: The threats posed by air pollution and climate change have resulted in considerable public debate about forest condition and growth during the past two decades. Despite the massive input ofresearch resources, no clear answers have been found to these global questions. Although there have been substantial advances in our knowledge of the effects of air pollutants on the forests, many of the questions associated with forest condition are still open. Monitoring of forest condition at the national level started in Finland in 1985 in accordance with the methodology drawn up by the International Co-operative Programme on Assessments and Monitoring of Air Pollution Effects on Forests (ICP Forests, UN/ECE). Since then, research into forest condition and vitality has been one of the key areas in the research carried out by the Finnish Forest Research Institute. Three basic questions formed the starting point for the multidisciplinary, Forest Condition Research Programme: What changes are taking place in our forests? Why does forest condition vary, and why do trees appear to be suffering? How can forest condition be maintained through appropriate forest management? This report covers forest condition and changes in environmental factors on the of the latest findings, publications and expertise of researchers participated in basis the Forest Condition Research Programme. In addition to researchers from the Finnish Forest Research Institute, a large number of scientists from domestic and foreign universities and research institutes also made a considerable contribution to the research programme.