Biohydrogen: Advances in Theory and Production is a comprehensive guide to the theory and methodology of biohydrogen production, highlighting its potential to contribute to a sustainable and eco-friendly society. The book explores the environmental advantages of biohydrogen over other energy sources and its role in reducing CO2 emissions, making it a crucial component in the transition to renewable energy. It systematically introduces the production processes, including biophotolysis, microbial electrolysis cells, photo-fermentation, dark fermentation, and combined dark-photo fermentation. Each chapter discusses a different method for biohydrogen production, covering the theory and methodology, substrate types, reactor structures, operational parameters, and net zero effects. The book also includes case studies of actual biohydrogen production projects, providing practical insights and real-world applications for each production method. Additionally, it provides an economic analysis and sustainability of biohydrogen production, comparing different methods via life cycle assessment and discussing the environmental and socio-economic risks.