Fermentation is an important innovation by mankind and this process is used for converting organic substrate into useful products. Using natural conditions, specifically, light and dark conditions, photo-fermentation and dark fermentation techniques can be developed and operated under controlled conditions. Generally, products such as biofuels, bioactive compounds and enzymes have been produced using the dark fermentation method. However, the major requirement for today's industralized world is biofuels in its clean and pure forms. Biohydrogen is the most efficient and cleanest form of energy produced using dark fermentation of organic substrates. Nevertheless, the quantity of biohydrogen produced via dark fermentation is low. In order to increase the product quantity and quality, several internal and external stress or alterations are made to conventional fermentation conditions. In recent times, nanotechnology has been introduced to enhance the rate of dark fermentation. Nanoparticles (NPs), specifically, inorganic NPs such as silver, iron, titanium oxide and nickel have increased the production rate of biohydrogen. Therefore, the present review focuses on exploring the potential of nanotechnology in the dark fermentation of biohydrogen production, the mechanisms involved, substrates used and changes to be made to increase the production efficiency of dark fermentation. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.