Some microalgae and cyanobacteria can oxidize water at photosystem II on one hand and reduce protons into dihydrogen at hydrogenase level on the other hand, using sunlight as energy input and the photosynthetic machinery as an energy converter. Such a phenomenon is envisaged as a potential friendly way to renewably and environmentally produce hydrogen as an energy carrier for human needs. However, hydrogen production by photosynthetic oxygenic microorganisms faces two major limitations: oxygen sensitivity of hydrogenases and competitive use of photosynthesis-generated reducing power by other physiological functions. A first strategy in order to overcome these deadlocks is to try to improve oxygen tolerance of hydrogenases. A site-directed mutagenesis approach undertaken on the Desulfovibrio fructosovorans enzyme has shown that this could be achieved in NiFe hydrogenases and might therefore bring new prospects for cyanobacterial hydrogenase improvement. A second strategy is to take advantage of metabolic flexibility of microorganisms. In cyanobacteria and in chloroplasts of microalgae, different “respiratory-like” electron transfer pathways interact with the photosynthetic electron transfer chain. By analyzing gas exchange of the microalga Chlamydomonas reinhardtii and of the cyanobacterium Synechocystis PCC6803 using membrane-inlet mass spectrometry, we have shown these pathways also interact with hydrogen metabolism. Their inhibition or stimulation, depending on the features and context of hydrogenase function, may be designed in order to alleviate hydrogenase exposure to O₂ and/or to increase the portion of photosynthetic electron transfer susceptible to be derived into H₂ production in fine. We will give an overview of the approaches that we have conducted in order to unravel the key components and limitations of these pathways, and, as a consequence, of some strategies which can be devised for enhancing hydrogen production potential in photosynthetic microorganisms.