As obnoxious as it may sound, studies involving human excreta are of great importance to sanitation, one of the most effective ways by which public health can be improved. The composition of human excreta is highly variable and contains all that enters into the toilet including water, urine, anal cleansing materials, lipids, proteins, polysaccharides, chemical elements, and undigested food residues as well as municipal wastes. A great deal of past and present research has focused on efficient utilization of this waste product of the human digestive system, particularly in biological processes, such as anaerobic digestion, where the waste is used as substrate to produce value-added products like biogas. However, there is very limited data on the chemistry of human excreta and its direct impact on anaerobic digestion process efficiency. This review therefore aims to illustrate the significance of the chemistry of human excreta relevant to biogas production and discuss key criteria and values that will help advance research and development of anaerobic digestion systems using human excreta as a treatment technology.