Hydrogen systems can provide viable, sustainable options for meeting the world's energy requirements. Hydrogen is relevant to all of the energy sectors-transportation, buildings, utilities and-industry. It can provide storage options for baseload (geothermal), seasonal (hydroelectric) and intermittent (PV and wind) renewable resources, and when combined with emerging decarbonization technologies, can reduce the climate impacts of continued fossil fuel utilization. However, hydrogen energy systems still face a number of technical and economical barriers that must first be overcome for hydrogen to become a competitive energy carrier. Advances must be made in hydrogen production, storage, transport and utilization technologies and in the integration of these components into complete energy systems. To expedite the advancement of hydrogen technologies and realize a hydrogen future, nations have come together under the auspices of the International Energy Agency's (IEA) Hydrogen Program to collaborate and address the important barriers that impede hydrogen's worldwide acceptance. Through well-structured, collaborative projects, experts from around the world address many of the technical challenges and long-term research needs that face the hydrogen community. These collaborations have already led to significant advances in renewable hydrogen production and solid storage materials and to the development of tools to evaluate and optimize integrated hydrogen energy systems. (C) 2003 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy.