Sewage waste water is a major area of concern in highly urbanized localities. The elimination of the contaminants dissolved in waste water are a heated topic. The untreated sewage gets directly discharged into the main rivers resulting in the eutrophication and biological toxicity to living ones. With the advent of the improved fermentation technologies the anaerobic sewage treatment plants are flourishing. Biochemical, microbiological, and digester technological advances in anaerobic technology has shown some promising results in the sewage stabilization. One of the most significant aims of using anaerobic process is that low maintenance, very minimal requirement of micro–macro nutrients and production of relatively low sludge. Anaerobic digestion is done if BOD/COD is 0.5 or higher; high temperature of effluents; presence of cyanides, phenols, heavy metals, long chain fatty acids, ammonia and sulphides sometimes inhibit the process. Different types of the digesters are installed for the anaerobic treatment of industrial effluents such as UASB, Anaerobic baffled reactor, Anaerobic sequencing batch reactor, anaerobic filters, expanded and fluidized bed reactor etc. But much work in this field is needed because of lack of awareness. Therefore, this chapter is aimed to focus on the different anaerobic microbes and their biochemistry associated with anaerobic digestion. This chapter also outlines the various reactor deployed for anaerobic digestion of the sewage waste water and the factors affecting the working of digesters.