Todays, the greatest source of energy is supplied by fossil fuels, particularly oil. Burning of fossil fuels is associated with environmental problems, and also the resources of these fuels are limited. One of the new and effective resources of energy is biofuel cells, which is a solution for clean and renewable energy. It generates electrical energy by biological catalysts as microorganisms or enzymes. In this paper, classification, mechanism, and the favorable applications of biofuel cells are discussed. Then, the obtained results and the recommendations for further research studies in this topic are discussed.