Dark fermentation is the fermentative conversion of organic substrate to biohydrogen, it is a complex process manifested by diverse group of bacteria by a series of biochemical reactions involving three steps similar to anaerobic conversion. Dark fermentation differs from photofermentation because it proceeds without the presence of light. Fermentative/hydrolytic microorganisms hydrolyze complex organic polymers to monomers which further converted to a mixture of lower molecular weight organic acids and alcohols by obligatory H2 producing acidogenic bacteria. Utilization of wastewater as a potential substrate for biohydrogen production has been drawing considerable interest in recent years especially in dark fermentation process.