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The idea of sustainable development, which was officialised by the Brundtland Report in 1987, was born from the will to reconcile the defence of ecological equilibria with the necessity to offer better conditions of life to the developing countries. It was supported from the start by the most important ecological NGOs. Following Solow, economists showed that, under specific conditions, economic growth was not conducive to environmental degradation. In 1992, the Rio de Janeiro Conference transformed sustainable growth into a political obligation for political authorities, whatever their scale. Because of the urgency created by climatic change, targets were fixed at the top level, and then applied to every State. Other procedures, which give more initiative to the local and national levels, are also used.