Accelerating, human-induced changes in global natural systems, with global warming as a prime example, are modifying international relations. Diplomacy has to recognize that new types of threats will require new solutions and a new spirit of cooperation. This is a gradual process, traditional conflicts will continue to haunt the international system and traditional methods of diplomatic work still prevail. Based on forty years of experience in multilateral negotiations as former diplomat and international negotiator, the author has developed the concept of a New Diplomacy for Sustainable Development. The book develops the theoretical foundations of the concept and links it to the notion of enabling conditions, describing the close linkages between domestic policies and international negotiations. In conclusion, Kjellen comments on present negotiation processes and offers ideas for institutional reform of the international system.