Biohydrogen is a promising gaseous biofuel that has prospective applications in combined heat and power, for fuel cells, or as a precursor for chemicals production. Hydrogen can also be converted to liquid hydrocarbon fuels and value-added chemicals through catalytic thermochemical or through biocatalytic biological pathways. This book addresses both the fundamentals as well as advanced new technological research on biohydrogen production by focusing on recent global research with emphasis on the technological, environmental, socioeconomic, and techno-economic aspects. It covers some the important advances in the production and utilization of biohydrogen and its solutions for clean fuel, waste management, waste valorization, reduced greenhouse gas emissions, and climate change mitigation. The book first covers the basic principles, benefits, and challenges concerning both the biological and thermochemical routes for biohydrogen production and then goes on to address topics such as biomass conversion to hydrogen through gasification with a focus on the process parameters, catalytic reforming technologies for hydrogen production concerning various feedstocks, the co-conversion of plastic wastes and biomass into biohydrogen through co-gasification technology, the effect of process parameters on syngas yields through co-gasification; fermentative hydrogen production technologies, the molecular mechanism of hydrogen production and enhancing the yield in hydrogen production by genetic and metabolic engineering, hydrogen production routes through microbial electrolysis, and much more.