This review discusses the potential role of hydrogen and fuel cells in the global energy system, highlighting their potential for decarbonisation across electricity, heat, industry, transport, and energy storage. While hydrogen technologies have faced cycles of high expectations followed by disillusionment, recent advancements in cost and performance suggest economic viability. The paper assesses the current status of hydrogen in fulfilling its potential, noting that hydrogen is well established in certain niches, such as forklift trucks, while mainstream applications are emerging. Hydrogen vehicles are commercially available in several countries, with over 225,000 fuel cell home heating systems sold, representing a significant shift from five years ago. Challenges around cost and performance remain, but the medium-term future of hydrogen as a competitive energy source is no longer unrealistic. Hydrogen and fuel cells are experiencing a resurgence in interest due to technological improvements, commercial product availability, and a strengthened global resolve to mitigate climate change. The paper provides a comprehensive state-of-the-art update on hydrogen and fuel cells across transport, heat, industry, electricity generation, and storage, covering technologies, economics, infrastructure requirements, and government policies. It defines the many roles these technologies can play in the near future as flexible and versatile complements to electricity, offering end-users more choice in decarbonising energy services. The review covers the transport sector, heat production, electricity sector integration, infrastructure needs, and policy challenges. It discusses the suitability of hydrogen and fuel cells in various transport modes, noting that hydrogen is one of three main options for low-carbon transport alongside biofuels and electric vehicles. Hydrogen vehicles can improve air quality, addressing urgent priorities such as reducing premature deaths from particulates and NOx emissions. The paper also discusses hydrogen powertrains, comparing them to alternatives in terms of cost, range, refuelling time, infrastructure requirements, lifetime, user experience, emissions, and network requirements. The review highlights the potential of hydrogen in various sectors, including passenger cars, refuelling stations, other road transport, off-road transport, heat and industry, and the power system. It discusses the challenges and opportunities for hydrogen in these sectors, noting that while hydrogen has the potential to play a significant role in decarbonising the energy system, challenges around cost, performance, and infrastructure remain. The paper concludes that hydrogen and fuel cells are seeing a resurgence in interest, with significant progress in technological development and commercialisation, and that their role in the global energy system is likely to grow in the coming decades.This review discusses the potential role of hydrogen and fuel cells in the global energy system, highlighting their potential for decarbonisation across electricity, heat, industry, transport, and energy storage. While hydrogen technologies have faced cycles of high expectations followed by disillusionment, recent advancements in cost and performance suggest economic viability. The paper assesses the current status of hydrogen in fulfilling its potential, noting that hydrogen is well established in certain niches, such as forklift trucks, while mainstream applications are emerging. Hydrogen vehicles are commercially available in several countries, with over 225,000 fuel cell home heating systems sold, representing a significant shift from five years ago. Challenges around cost and performance remain, but the medium-term future of hydrogen as a competitive energy source is no longer unrealistic. Hydrogen and fuel cells are experiencing a resurgence in interest due to technological improvements, commercial product availability, and a strengthened global resolve to mitigate climate change. The paper provides a comprehensive state-of-the-art update on hydrogen and fuel cells across transport, heat, industry, electricity generation, and storage, covering technologies, economics, infrastructure requirements, and government policies. It defines the many roles these technologies can play in the near future as flexible and versatile complements to electricity, offering end-users more choice in decarbonising energy services. The review covers the transport sector, heat production, electricity sector integration, infrastructure needs, and policy challenges. It discusses the suitability of hydrogen and fuel cells in various transport modes, noting that hydrogen is one of three main options for low-carbon transport alongside biofuels and electric vehicles. Hydrogen vehicles can improve air quality, addressing urgent priorities such as reducing premature deaths from particulates and NOx emissions. The paper also discusses hydrogen powertrains, comparing them to alternatives in terms of cost, range, refuelling time, infrastructure requirements, lifetime, user experience, emissions, and network requirements. The review highlights the potential of hydrogen in various sectors, including passenger cars, refuelling stations, other road transport, off-road transport, heat and industry, and the power system. It discusses the challenges and opportunities for hydrogen in these sectors, noting that while hydrogen has the potential to play a significant role in decarbonising the energy system, challenges around cost, performance, and infrastructure remain. The paper concludes that hydrogen and fuel cells are seeing a resurgence in interest, with significant progress in technological development and commercialisation, and that their role in the global energy system is likely to grow in the coming decades.