Extracellular electron transport (EET) is a biological process where microorganisms can donate electrons from the interior of their cells to external electron acceptors or act as electron acceptors to receive electrons from external sources and electrodes. This process often occurs in the surrounding environment or within biofilms, enabling the redox reactions essential for energy metabolism. This review evaluates the latest developments in electron transfer (EET) research in environmental biotechnology, showcasing its varied applications across bioelectrochemical systems (BES), including microbial fuel cells and microbial electrosynthesis for CO