In his 2003 State of the Union address, President Bush announced a hydrogen initiative to reverse America's growing dependence on foreign oil and improve the environment. The President urged the development of commercially viable fuel cells for cars, truck homes, and businesses. A transition to hydrogen as a major fuel in the next 50 years could fundamentally transform the U.S. energy system, creating opportunities to increase energy security through the use of a variety of domestic energy resources for hydrogen production while reducing environmental impacts, including atmospheric CO2 emissions and criteria pollutants. This book provides information on the Department of Energy's (DOE) hydrogen program which has made important progress in all research and development areas, including both fundamental and applied science. Specifically, the DOE has reduced the cost of producing hydrogen from natural gas, an important source of hydrogen through the next 20 years, developed a sophisticated model to identify and optimize major elements of a projected hydrogen delivery infrastructure, increased the storage capacity of hydrogen by 50%, and reduced the cost and improved the durability of fuel cells. However, some of the most difficult technical challenges lie ahead, including reducing the cost of delivering hydrogen to consumers, and further reducing the cost and improving the durability of fuel cells. The difficulty of overcoming these technical challenges, as well as hydrogen research and development budget constraints, has led the DOE to push back some of its interim target dates.