Why is hydrogen an energy carrier? How do fuel cells work? How will we use hydrogen in future vehicles? How safe is the technology? This compact book clearly describes the physical and chemical fundamentals of hydrogen technology and explains the expected technical solutions. It presents the challenges and allows for a better understanding of the efforts by industry and research towards the widespread adoption of this technology. The authors vividly explain the functioning of the key components in the conversion chain from renewable electricity to vehicle propulsion and highlight their technical development potentials. Considering reliability and cost-effectiveness, they assess the sustainability of the energy cycle that can be achieved with hydrogen as an energy carrier.