Electron transfer between microorganisms and an electrode — even across long distances — enables the former to live by coupling to an electronic circuit. Such a system integrates biological metabolism with artificial electronics; studying these systems adds to our knowledge of charge transport in the chemical species involved, as well as, perhaps most importantly, to our knowledge of charge transport and chemistry at the cell–electrode interfaces. This understanding may lead to microbial electrochemical systems finding widespread application, particularly in the energy sector. Bioelectrochemical systems have already shown promise for electricity generation, as well as for the production of biochemical and chemical feedstocks, and with improvement are likely to give rise to viable applications.