"Preface Purpose and Audience Hydrogen shows great promise both as an energy carrier and as a fuel for transportation, portable, and stationary sources; however, the expanded use of hydrogen as a renewable energy source raises a number of concerns and challenges that complicate planning efforts. Organizations are researching, developing, and validating hydrogen pathways to establish a business case for market implementation. However, significant research and educational challenges still must be addressed. The use of hydrogen technologies addresses critical societal issues related to energy security, stability, and sustainability. First, hydrogen may be produced from local resources, thus eliminating the need for complex energy/fuel supply lines. Second, hydrogen, used in conjunction with renewable energy sources, provides a stable method of energy/fuel production. Third, hydrogen produced from renewable sources provides clean, emission-free energy/fuel. Hydrogen technology constitutes a highly interdisciplinary field that extends from the fundamentals of materials, electrochemical processes, and fuel processing/storage systems, to complex design concepts for hybrid vehicles, and renewable power/fuel systems. Infrastructure analysis, market transformation, public policy, safety, and environment also play key roles. Additionally, sustainable energy systems is an emerging field that aims to develop new and improved energy technologies, systems, and services, while understanding the impact of energy on the economy and society. Hydrogen technology research encompasses traditional engineering disciplines (biological, chemical, electrical, environmental, geological, material science, mechanical, systems), sciences (biology, chemistry, mathematics, physics)"--