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Biohydrogen is a promising low-carbon energy source due to its high energy density, and emerging technologies have been studied to achieve highly efficient and competitive H2 production. The biological hydrogen production involves microbe-assisted bioconversion, either in the presence or in the absence of light, called photo-fermentation or dark fermentation, respectively. Biohydrogen production using fermentative conversion of organic carbon in the absence of light, i.e., dark fermentation, has gained great interest during the last few decades. The mechanistic understanding of various metabolic pathways involved in dark fermentative hydrogen production is well understood and reviewed here. Further, the hydrogen yield is affected by a number of factors during the fermentation of organic substrates by either pure or mixed microbial cultures, and some of the pertinent factors have been discussed in this review. This review aims to present the current state of knowledge on the dark fermentation process, focusing on the use of waste materials as substrates. [ABSTRACT FROM AUTHOR]