Atmospheric pollution attributed to increased combustion of fossil fuels has been implicated as a likely contributing factor in observed changes to forests in North America and Europe. Uncertainties surrounded the mechanisms and specific causes for these changes have prompted intensified interest in research on air pollution effects on forests. Major objectives of the review are: To provide a conceptual and historical perspective against which today's problems, concerns, and approaches can be evaluated; To evaluate evidence of changes in growth and vitality of some tree species in today's forests; To compare levels of principal atmospheric pollutants in Europe and the U.S.; To describe mechanisms, pathways, and concentration thresholds for effects of principal pollutants on tree growth and physiology; To summarize current evidence for the role of pollution in observed forest declines; and To provide some perspectives on future research in this area. (Copyright (c) 1985-Air Pollution Control Association).