This, the 6th International Symposium on Sustainable Minerals (Sustainable Minerals '21), is the postponed Sustainable Minerals '20, which was affected by the Coronavirus outbreak. It is organised by MEI in consultation with Prof Markus Reuter and is sponsored by FLSmidth. Media sponsors are International Mining and the Coalition for Eco-Efficient Comminution (CEEC) and the Cornwall Mining Alliance are Industry Associates.