In the late 1960s, Scandinavian scientists asserted that the long-range air pollution was causing serious acidification and that emissions all over Europe would have to be diminished. The prevailing view at the time was that air pollution was a local phenomenon best handled by building high smokestacks, and the major polluting countries were opposed to spending money on protecting areas far away in other countries. This chapter analyses how the discovery of “acid rain” triggered the first international research projects to confirm long-range air pollution and how, in a second phase, international negotiations involving scientists, policymakers, and diplomats resulted in the Convention on Long-Range Transboundary Air Pollution in 1979. Later on, special protocols were adopted, and the signing nations promised to decrease their emissions in accordance with specific goals. Cold War politics played an interesting role in the negotiations and led to an unexpected alliance between Nordic countries and the Soviet Union.