The World is facing an imminent shift from the present unsustainable energy system, primarily based on the utilization of fossil fuels. While there is still no firm consensus on the matter, our present state of knowledge and technological development tell us that only renewable energy sources have the potential to satisfy all the energy needs in a sustainable way. As an energy storage medium and as a major transportation fuel, hydrogen can play a significant role in such an energy system. Indeed only hydrogen has the potential to satisfy the energy storage and transportation needs on the scale that would be required in any future global energy sys- tem based on renewable energy sources. Hydrogen and fuel cells comprise a complex array of technologies and processes for hydrogen production, storage, transportation, distribution, fuel cell concepts and other end-use technologies. Some of these technologies are still under development and surrounded with considerable uncertainty. Realistic assessments and policy strategies for hydrogen and fuel cells must consider the complexity of the overall system, the uncertainties, the peculiarities of each single technology, the role of the competing options, and not least the impact that energy policies may have on new technologies to gain market share.