Hydrogen is widely accepted as a potential substitute for fossil fuels. Biological hydrogen production stands out as an environmentally harmless process carried out under mild operating conditions, using renewable resources. This book introduces the biological hydrogen production concept to the reader by providing a general knowledge on the subject. Then, original research results were presented and discussed. These include the effects of the physiological conditions such as the nutrient media composition on hydrogen production in photosynthetic bacteria, and the improvement of the photobioreactors by introduction of innovative elements to the design, manufacture and process control. Lastly, the parameters affecting the outdoor processes are identified and the results of the test runs done in outdoor conditions under sunlight illumination were evaluated. The results, analyses and discussions should be useful to researchers, engineers, biologists, academicians, college students or anyone else who may be interested in clean energy, biohydrogen production, photofermentation technology, photobioreactor development fields.