A cathode is the place where hydrogen is actually produced in MECs. Hydrogen evolution reaction (HER) on the cathode surface is not thermodynamically favorable; thus the use of suitable catalysts is necessary to facilitate HER to achieve high H2 production. Various cathode catalysts have been tested in MECs to date, and unlike water electrolyzers, cathode catalysts for MECs should be designed to work well under neutral pH conditions due to microbial activities. In the early stages of MEC studies, the Pt cathode was popularly used due to its excellent catalytic activities toward HER. However, the use of Pt in MECs is not practical due to its very high price. Thus, alternative cathode catalysts have been recently studied for MECs. Since it is thermodynamically impossible to overcome the catalytic activities of Pt with other non-precious cathode catalysts, alternative cathode catalysts have been developed in two directions: (1) synthesizing metal catalyst composites and (2) providing larger active surface areas for catalysts. Non-precious metal catalysts like nickel, molybdenum, and stainless steel were popularly studied in MECs. Carbon-based cathode materials such as activated carbon and carbon nanomaterials were studied as well to provide large and robust catalytic surface area for metal catalysts.