Hydrogen is seen as a "fuel of the future" that will replace the petroleum-based economy. It is a versatile energy carrier with the potential for extensive use as a transportation fuel, in power generation, and in many other applications. Hydrogen is currently produced from fossil sources (steam reforming of methane), but technologies utilizing renewable sources are urgently needed for sustainability. Biological hydrogen (biohydrogen) production is one of the challenging areas of technology development for sustainability. There are a wide range of biohydrogen technologies, including direct biophotolysis, indirect biophotolysis, photo-fermentations, and dark-fermentation. The current scientific results are promising, but substantial improvements in biohydrogen production through research advances (i.e. improvement in efficiency through genetically engineered microorganism, development of bioreactors etc.) are needed. In this study, attempts have been made to highlight not only the advantages, but also the bottlenecks that limit biohydrogen production.