Bioelectrochemical systems (BESs), such as microbial fuel/electrolysis cells, are promising wastewater treatment and energy generationapproaches that use electrochemically active bacteria (EAB). Bacteria growth in BES is a critical factor that controls the performance of the overall system. A magnetic field (MF) is an effective way to accelerate biofilm formation and extracellular electron transfer (EET). The performance is highly dependent on the MF intensity, exposure time, shape and orientation of the magnets, and the microbial structure of the inoculum. Despite the increasing number of investigations into each factor, there is an insufficient comprehensive understanding of the mechanism of MFs in BESs. In this review, the basic mechanism of MFs, as well as the various attempts to use MFs in BESs, and their effect on the obtained performances are introduced. Particularly, the empirical effects of MF on the EAB growth, EET, enzyme activity, and BES performance. Moreover, the influence of MF on radical pairs was also interpreted to explain how MF affects EET. This review is the first attempt at understanding the background and current trends in the application of MF technologies in BESs.