Contents. Acknowledgements. Summary. 1. Introduction (G.J. Heij). 2. Ammonia Emissions and Abatement (G.J. Heij, J.W. Erisman and J.H. Voorburg). 3. Concentration and Deposition of Acidifying Compounds (J.W. Erisman and G.J. Heij). 4. Effects of Air Pollution and Acid Deposition on Forests and Forest Soils (G.J. Heij, W. de Vries, A.C. Posthumus and G.M.J. Mohren). 5. Effects on Heathland (H. van Dobben). 6. Scenario Analyses Using the Dutch Acidification Systems Model (T.N. Olsthoorn, K.F. de Boer, R. Thomas, W. de Vries, J. Kros, C. van der Salm and J.C. Voogd, J.J.M. van Grinsven, J.G. van Minnen, C van Heerden, G.W. Heil, F. Berendse, A.H. Bakema, F.G. Wortelboer). 7. Critical Loads and Critical Levels for the Environmental Effects of Air Pollutants (W. de Vries and G.J. Heij). Annex 1: Thematic Reports. Annex 2: Review Report. Annex 3: Projects and Publications First and Second Phase Dutch Priority Programme on Acidification.