Bioelectrochemical systems are engineered systems in which the electronic transfer chain associated with microbial respiration is short-circuited. Electrons that would naturally flow from the substrate toward oxygen or another electron acceptor are collected at an electrode, on which the micro-organisms form a biofilm. Like in all fuel cells, the anodic reaction is coupled to an electron consuming reaction at a cathode. If the oxidation of organic matter at a bioanode is coupled to the reduction of oxygen at the cathode, the positive cell potential and the flow of electrons results in electricity production. Alternatively, oxidation of organics is coupled to hydrogen production (water splitting). The valorisation of organic wastes by electricity or hydrogen production is the usually foreseen application of bioelectrochemical systems. The use of bioelectrochemical systems for metal recovery by BioelectroMET is a completely novel approach.