SUN - Symbiosis Users Network (the Italian Network of Industrial Symbiosis), the CTS of Ecomondo and ENEA organized the fifth edition of the conference of the entitled "The contribution and potential of Industrial Symbiosis for the ecological transition". The conference was held on 27 October 2021. This event represented an opportunity for discussion on concrete cases of industrial symbiosis, on technical and/or operational standards and on tools to support both implementation and investments for industrial symbiosis. Many of the contributions presented by the scientific and business community on that day are collected in these proceedings.