Kalundborg Symbiosis is the world’s first working industrial symbiosis. An industrial symbiosis is a local collaboration where public and private enterprises buy and sell residual products in terms of materials and energy, resulting in mutual economic and environmental benefits. The Kalundborg Symbiosis is an industrial ecosystem, where the residual product of one enterprise is used as a resource by another enterprise, in a closed cycle. This collaborative approach adds value, reduces costs and improves environmental performance through the closing of material and energy cycles.