The U.S. Department of Energy and the National Renewable Energy Laboratory are developing technologies to produce hydrogen from renewable, sustainable sources, aiming for a cost goal of $2.00–$3.00 kg$^{-1}$ of hydrogen to make it cost-competitive with gasoline for passenger vehicles. Electrolysis of water is a standard commercial technology, and using wind and solar resources to generate the electricity for this process creates a renewable system. Biomass-to-hydrogen processes, including gasification, pyrolysis, and fermentation, are less well-developed but offer the potential to produce hydrogen from energy crops and biomass materials. Solar energy can be used to produce hydrogen from water and biomass through several conversion pathways, such as concentrated solar energy for thermochemical reactions, photoelectrochemical water splitting, and photobiology. All these technologies are in the development stage. The electrolysis of water is a reliable and clean method for producing hydrogen, with the potential to produce ultra-pure hydrogen. Electrolyzers can be categorized into alkaline and polymer electrolyte membrane (PEM) types, with PEM electrolyzers offering higher current densities and efficiency but requiring more expensive materials. Integrating electrolyzers with renewable energy systems can provide low-cost, environmentally friendly electricity and hydrogen, with the U.S. having significant potential for wind and solar resources. Biomass-to-hydrogen processes, such as gasification, pyrolysis, and reforming, offer a near-term option for hydrogen production. Gasification systems can produce hydrogen from lignocellulosic biomass, with theoretical yields of up to 17%. Pyrolysis and reforming of bio-oil can also produce hydrogen, with potential yields of up to 13%. Fermentation is a viable alternative for sustained hydrogen production, with microbes like Escherichia coli and Clostridial species capable of producing hydrogen. However, technical barriers such as high feedstock costs and low hydrogen molar yields need to be addressed. Research is ongoing to improve these processes, including the development of microbes that can utilize hemicellulose and cellulose directly and genetic engineering to optimize metabolic pathways. Solar-driven thermochemical reactions, such as those using concentrating solar systems, can efficiently split water into hydrogen and oxygen. These processes require high temperatures, typically achieved through solar collectors, and have the potential to be carbon-neutral and renewable. However, challenges include the high costs of solar collectors and the complexity of integrating the chemical processes with solar cycles. Photoelectrochemical water splitting and photobiology are long-term options for producing hydrogen from water using solar energy, with the potential to harness the entire visible spectrum for the reaction. Research in these areas is ongoing to overcome technical barriers and improve efficiency.The U.S. Department of Energy and the National Renewable Energy Laboratory are developing technologies to produce hydrogen from renewable, sustainable sources, aiming for a cost goal of $2.00–$3.00 kg$^{-1}$ of hydrogen to make it cost-competitive with gasoline for passenger vehicles. Electrolysis of water is a standard commercial technology, and using wind and solar resources to generate the electricity for this process creates a renewable system. Biomass-to-hydrogen processes, including gasification, pyrolysis, and fermentation, are less well-developed but offer the potential to produce hydrogen from energy crops and biomass materials. Solar energy can be used to produce hydrogen from water and biomass through several conversion pathways, such as concentrated solar energy for thermochemical reactions, photoelectrochemical water splitting, and photobiology. All these technologies are in the development stage. The electrolysis of water is a reliable and clean method for producing hydrogen, with the potential to produce ultra-pure hydrogen. Electrolyzers can be categorized into alkaline and polymer electrolyte membrane (PEM) types, with PEM electrolyzers offering higher current densities and efficiency but requiring more expensive materials. Integrating electrolyzers with renewable energy systems can provide low-cost, environmentally friendly electricity and hydrogen, with the U.S. having significant potential for wind and solar resources. Biomass-to-hydrogen processes, such as gasification, pyrolysis, and reforming, offer a near-term option for hydrogen production. Gasification systems can produce hydrogen from lignocellulosic biomass, with theoretical yields of up to 17%. Pyrolysis and reforming of bio-oil can also produce hydrogen, with potential yields of up to 13%. Fermentation is a viable alternative for sustained hydrogen production, with microbes like Escherichia coli and Clostridial species capable of producing hydrogen. However, technical barriers such as high feedstock costs and low hydrogen molar yields need to be addressed. Research is ongoing to improve these processes, including the development of microbes that can utilize hemicellulose and cellulose directly and genetic engineering to optimize metabolic pathways. Solar-driven thermochemical reactions, such as those using concentrating solar systems, can efficiently split water into hydrogen and oxygen. These processes require high temperatures, typically achieved through solar collectors, and have the potential to be carbon-neutral and renewable. However, challenges include the high costs of solar collectors and the complexity of integrating the chemical processes with solar cycles. Photoelectrochemical water splitting and photobiology are long-term options for producing hydrogen from water using solar energy, with the potential to harness the entire visible spectrum for the reaction. Research in these areas is ongoing to overcome technical barriers and improve efficiency.