Symbiosis means co-existence between diverse organisms in which each may benefit from the other. In the ancient harbor town of Kalundborg, Denmark, various processing companies, a waste handling company, and the Municipality of Kalunborg participate in industrial symbiosis. All participants exploit each other's residual or by-products mutually. The symbiosis co-operation self-organized over a number of decades and today comprises some 20 projects. The main resources circulated among the partners are steam, gas, cooling water, and gypsum. Excess heat is used for fish farming, heating of nearby homes, and greenhouse agriculture. Other by-products not usable within the industrial park, such as sulfur, fly ash, and sludge, are sold to companies in the vicinity. One company's by-product becomes an important resource to one or several of the other companies. The outcome is reduced consumption of resources and a significant reduction in environmental strain.Main participants: Energy E2 Asnæs Power Station, the plasterboard factory BPB Gyproc A/S, the pharmaceutical plant Novo Nordisk A/S, the enzyme producer Novozymes A/S, the oil refinery Statoil A/S, Bioteknisk Jordrens Soilrem A/S as well as the waste company Noveren I/S and Kalundborg Municipality.