Mixed culture biotechnology (MCB) could become an attractive addition or alternative to traditional pure culture based biotechnology for the production of chemicals and/or bioenergy. On the basis of ecological selection principles, MCB-based processes can be established that generate a narrow product spectrum from a mixed substrate. Three example processes are briefly discussed in this paper: anaerobic digestion aimed at the production of methane-containing biogas, mixed culture fermentation for the production of solvents or biohydrogen, and a two-step process for the production of polyhydroxyalkanoates. These examples give an idea of the potential contribution of mixed culture biotechnology to sustainable production of bioenergy from waste.