The reduction of humus and metals such as Fe and Mn is a challenge for microorganisms, as these substances have low water solubility and cannot enter into cell envelopes. Extracellular electron transfer is defined as the process through which electrons derived from the oxidation of electron donors are transferred from the inner membrane to the outer membrane of the cell to reduce an extracellular terminal electron acceptor. S. oneidensis MR-1 and G. sulfurreducens are the most frequently used organisms for extracellular respiratory bacteria experiments because they have developed electron transfer strategies that require mutiheme c-type cytochromes (c-Cyts). In S. oneidensis MR-1, multiheme c-Cyts, CymA, and MtrA are believed to transfer electrons from the inner membrane qunione/quinol pool through the periplasm to the outer membrane (OmcA, MtrC). The Type Ⅱ secretion system of S. oneidensis MR-1 was due to the direct involvement of translocation of MtrC and OmcA to the bacterial cell surface. The decaheme c-Cyts, MtrC, and OmcA can directly reduce the extracellular electron acceptors. Likewise, for G. sulfurreducens, MacA delivered electrons from the inner membrane to PpcA in periplasm, and PpcA subsequently transferred electrons to the OMCs (OmcB, OmcE, OmcS, and OmcZ) and Type Ⅳ pili that were hypothesized to relay the electrons to extracellular electron acceptors. This review summarizes the recent advances of extracellular electron transfer mechanisms with a focus on Shewanella and Geobacter.