Hydrogen (H2) has been considered as a sustainable energy carrier as it is clean (does not emit any toxic by-product or greenhouse gases), efficient, and renewable. Currently, H2 is being produced mainly from fossil fuels, biomass, and water. H2 production through biological routes is considered as one of the opportunistic and sustainable ways to meet the future energy demand and to prevent fossil fuel-based environmental impacts. Biological approaches for producing H2 also facilitate the conversion of negative-value organic waste. Broadly, biological H2 can be produced through two main mechanisms: photosynthesis and dark fermentation. Photosynthesis is a light-dependent process, while dark fermentation (anaerobic) is a light-independent catabolic process. Most of the biological H2 production processes are operated at ambient temperatures and pressures regarded as less energy intensive and therefore considered as a potential alternative to the conventional physical/chemical methods usually opted for H2 production. Biohydrogen can also be viewed as energy source and an intermediate towards the production of VFA (volatile fatty acids). VFA present in these effluents generated from H2 producing reactor can be further transformed to PHAs or can be used for biohydrogenation of fatty acids into alcohols.