The greatest concern for the world today is the environmental pollutions that is mainly taking place due to the rapid utilization of natural resources and industrialization. The most common root for this is the release of harmful gases by the combustion of fossil fuels, which causes various environmental issues. There is need to overcome these issues by developing advance and alternate energy sources, which can mimic this issues without any impact in the surroundings. Although the conventional fuels are depleting at a higher rate today like reserves of oil, coal and natural gas, therefore research is carried out for the sustainable environment for future generations. However, hydrogen assures to be a potential clean, renewable and environmental friendly energy source because of its easy conversion accessibility to electricity by fuel cells and it does not involve any emission of greenhouse gases like CO2, which are released from the combustion as a clean fuel. Biological hydrogen production generally can be carried out by two mechanisms-the fermentation and photo biological production. Photo biological hydrogen production has the advantage that utilizes solar radiation to run the operation but progressive reactor designs are required to achieve moderate solar radiation conversion efficiencies and H2 production rates. The process of fermentation utilizes free carbon as source of energy in agricultural by-products or wastes. However, the feasibility of fermentative hydrogen production depends upon the choice of the substrate. WHY BIOHYDROGEN: The sources of feedstocks for the production of bio hydrogen varies from process to process and the technology employed. The table below shows the comparison of the biological feedstocks used in the production of hydrogen and the technology employed to carry out the process. SOURCES OF BIOHYDROGEN PRODUCTION: The sources of feedstocks for the production of bio hydrogen varies from process to process and the technology employed. The table below shows the comparison of the biological feedstocks used in the production of hydrogen and the technology employed to carry out the process. ENZYMES: The production of biohydrogen as a future energy resource using potential microorganisms is due to a novel enzymes which can catalyze the reaction of hydrogen production. The family of enzymes that catalyze the reversible oxidation of hydrogen into its elementary particle constituents, two protons (HC) and two electrons is named as a Hydrogenase (Das et al., 2006): 2H+ 2e-→H2 Mainly two enzymes are involved in the production of hydrogen : hydrogenase [types of hydrogenases: (i) hup-encoded [NiFe]-uptake hydrogenases, (ii) hox-encoded [NiFe]-bidirectional hydrogenases (iii) [FeFe]-hydrogenases, (iv) [NiFeSe]-hydrogenases (as one of the Ni-bound cysteine residues of [NiFe]-hydrogenases is replaced by selenocysteine), and (iv) [Fe]-only hydrogenases]. and nitrogenase. Fe-hydrogenase enzyme is used in the biophotolysis processes, photo-fermentation processes utilize nitrogenase (Manish and Banerjee, 2007). Hydrogenase enzymes present in microalgae, cyanobacteria, and anoxygenic photosynthesis and fermentative bacteria while nitrogenase present in cyanobacterial heterocysts and purple non-sulphur bacteria (Meyer et al., 1978). Nitrogenases is complex enzyme made up of two subunits : (i) the reductase subunit and (ii) the dinitrogenase complex. PRODUCTION PROCESSES: Biological hydrogen production achieved by anaerobic and photosynthetic microorganisms using carbohydrate-rich and non-toxic raw materials, industrial waste,agricultural waste helps in development of eco-friendly and cleaner form of energy. Biohydrogen can be produced in both anerobic (a by-product during conversion of organic wastes into organic acids, which are then used for methane generation. The acidogenic phase of anaerobic digestion of wastes can be manipulated to improve hydrogen production) and Photosynthetic processes Photosynthetic processes include algae, which uses CO2 and H2O for hydrogen gas production and Some photo-heterotrophic bacteria utilize organic acids such as acetic, lactic, and butyric acids to produce H2 and CO2 (Kapdan and Kargi, 2006) there is difference in the yield. A successful biological conversion of biomass to hydrogen depends strongly on the processing of raw materials to produce feedstock, which can be fermented by the microorganisms (Li and Chen, 2007). Biological hydrogen production generally can be carried out by two mechanisms 1.Photo biological production (Bio photolysis) 1.1Indirect Bio photolysis This process consists of two stages i.e. photosynthesis for carbohydrate accumulation and dark fermentation of the carbon reserve for hydrogen production (Yu and Takahashi, 2007). In the initial stage the acidogenic bacteria present in the environment produce some hydrogen by degrading waste carbohydrate matter into simple organic acids and alcohols while in the next stage In the second stage these organic acids used as a substrate to photoheterotrophic bacteria for additional hydrogen production (Lee et al., 2007). 12H2O+6CO2+ Light energy → C6H12O6 + 6O2 C6H12O6 + 12H2O + Light energy → 12H2 + 6CO2 The mutant strains of A. Variabilis is developed which has potential of hydrogen production with the rate of the order of 0.355 mmol/h per liter (Manish and Banerjee, 2007) by indirect bio photolysis. The hydrogen production by Cyanobacteria has been studied for over three decades and the chemistry of production showed below.