Kalundborg Symbiosis is a partnership between 17 public and private companies in Kalundborg, Denmark. Since 1972, they have developed the world's first industrial symbiosis with a circular approach to production.

The main principle is that a residue from one company becomes a resource in another, benefiting both the environment and the economy. Such symbiosis creates growth in the local area and supports the companies' CSR efforts and climate change mitigation. The partners of Kalundborg Symbiosis have worked together since the 1960's, resulting in a collaborative approach and openness to new symbiosis opportunities.

By working together and exchanging material, water and energy streams between the partners, Kalundborg Symbiosis increases resilience and economic gains, while reducing the environmental impact and expenses. Building a functioning industrial symbiosis is not about working together for the sake of each other and the environment, but rather a continual search for a better way of doing business. Projects completed over the years range from algae production facilities to bio-ethanol production, with some projects already being implemented at larger scale.