The use of microalgae for production of hydrogen gas from water photolysis has been studied for many years, but its commercialization is still limited by multiple challenges. Most of the barriers to commercialization are attributed to the existence of biological regulatory mechanisms that, under anaerobic conditions, quench the absorbed light energy, down-regulate linear electron transfer, inactivate the H2-producing enzyme, and compete for electrons with the hydrogenase. Consequently, the conversion efficiency of absorbed photons into H2 is significantly lower than its estimated potential value of 12–13 % of sunlight. However, extensive research continues towards addressing these barriers by either trying to understand and circumvent intracellular regulatory mechanisms at the enzyme and metabolic level, or by developing biological systems that achieve prolonged H2 production albeit under lower than 12–13 % solar conversion efficiency. I will describe the metabolic pathways involved in biological H2 photoproduction from water photolysis, the attributes of the algal [FeFe]-hydrogenases, and highlight NREL research related to addressing some of these barriers, including: (a) the discovery of a new mechanism for regulation of H2 production; (b) recent advances in expressing in green algae a hydrogenase that is more tolerant to O2; (c) understanding the redox mediator responsible for linking photosynthetic electron transport to hydrogenases; (d) the development of a high-throughput assay to detect H2 production on plates.