Extracellular electron transfer (EET) is an important biological process in microbial physiology as found in dissimilatory metal oxidation/reduction and interspecies electron transfer in syntrophy in natural environments. EET also plays a critical role in microorganisms relevant to environmental biotechnology in metal-contaminated areas, metal corrosion, bioelectrochemical systems, and anaerobic digesters. species exist in a diversity of natural and artificial environments. One of the outstanding features of species is the capability of direct EET with solid electron donors and acceptors, including metals, electrodes, and other cells. Therefore, species are pivotal in environmental biogeochemical cycles and biotechnology applications. , a representative species, has been studied for direct EET as a model microorganism. employs electrically conductive pili (e-pili) and -type cytochromes for the direct EET. The biological function and electronics applications of the e-pili have been reviewed recently, and this review focuses on the cytochromes. species have an unusually large number of cytochromes encoded in their genomes. Unlike most other microorganisms, species localize multiple cytochromes in each subcellular fraction, outer membrane, periplasm, and inner membrane, as well as in the extracellular space, and differentially utilize these cytochromes for EET with various electron donors and acceptors. Some of the cytochromes are functionally redundant. Thus, the EET in is complicated. coordinates the cytochromes with other cellular components in the elaborate EET system to flourish in the environment.