Photo-fermentation refers to the synthesis of hydrogen gas (H₂) by hydrogen-producing microorganisms, typically photosynthetic bacteria, using light as an energy source. These bacteria utilize organic electron donors, such as organic acids, to generate hydrogen. This chapter presents the types of microbial communities involved in biological hydrogen production via photo-fermentation, the various fermentation pathways employed, as well as their applications and associated challenges. Techniques, scope of work, and future perspectives of biohydrogen production via photo-fermentation are also briefly discussed. Biohydrogen production via photo-fermentation is an attractive alternative to traditional hydrogen production techniques such as steam methane reforming or electrolysis, as it is both clean and sustainable. However, several challenges must be addressed to enable industrial-scale application. These include hydrogenase enzyme instability, oxygen sensitivity, and limited light efficiency at large scales. Despite these hurdles, this process holds significant potential for contributing to the hydrogen economy, especially if successfully integrated with renewable energy sources and optimized bioreactor designs. Advances in genetic engineering, metabolic engineering of microorganisms, and bioreactor technologies are expected to play a key role in improving the efficiency and scalability of biohydrogen production through photo-fermentation.