The U.S. Department of Energy and the National Renewable Energy Laboratory Lire developing technologies to produce hydrogen from renewable, sustainable sources. A cost goal of $2.00-$3.00 kg(-1) of hydrogen has been identified as the range at which delivered hydrogen becomes cost competitive with gasoline for passenger vehicles. Electrolysis of water is a standard commercial technology for producing hydrogen. Using wind and solar resources to produce the electricity for the process creates a renewable system. Biomass-to-hydrogen processes, including gasification, pyrolysis, and fermentation, Lire less well-developed technologies. These processes offer the possibility of producing hydrogen from energy crops and from biornass materials such as forest residue and municipal sewage. Solar energy can be used to produce hydrogen from water and biomass by several conversion pathways. Concentrated solar energy can generate high temperatures at which thermochemical reactions can be used to split water. Photoelectrochemical water splitting and photobiology are long-term options for producing hydrogen from water using solar energy. All these technologies Lire in the development stage. Copyright (C) 2007 John Wiley & Sons, Ltd.