The scientific and political value of experimental field studies of acidification processes have been well recognized for some time. There has been a large increase during the past decade in the amount of experimental research being conducted on the environmental effects of atmospheric deposition, especially of nitrogen (N). The experimental approach has shifted heavily into the area of whole-ecosystem experimental manipulations that have been and are being conducted across gradients of atmospheric deposition and other environmental factors throughout northern Europe. Whole-ecosystem experimental manipulations are needed across gradients of atmospheric deposition, climate, and other important factors. The obvious linkages between short-term climatic fluctuation and anthropogenic inputs of N and sulphur were incorporated into the experimental approach followed by the European Experimental MANipulation program. At each site, precipitation, throughfall, soil, soil solution, and runoff were monitored, before and after initiation of the experimental manipulations.