Hydrogen has a key role to play as a carbon-free energy carrier alongside electricity. Hydrogen can be transported worldwide by ship and pipeline and can be stored underground in large volumes. This makes it possible to deliver cheap renewable energy, especially solar and wind, cost efficiently at the right time and place to the customers. Next to this systemic role, hydrogen is important to decarbonize energy use in hard to abate sectors in industry, mobility, electricity balancing, and heating. Future hydrogen systems will have similar characteristics as present day natural gas systems. Large-scale multi-GW renewable hydrogen production plants at good resources sites will produce a minimum of 1 million tonnes hydrogen. Hydrogen infrastructure can be realized by re-using the gas infrastructure, pipelines, and salt cavern storage, without major adaptations. As a transition, hydrogen produced from fossil fuels at the resource sites with Carbon Capture and Storage directly in the field below, can bring low-carbon hydrogen volume in the system. Such an approach can establish a fast, cheap, and reliable transition to a sustainable energy system, whereby hydrogen will fully replace natural gas, coal, and oil. The conversion technology used today is based on combusting technologies: boilers, furnaces, engines, and turbines. These combustion technologies can be easily and are fast adapted to combust hydrogen. In future, however, combustion technologies will be replaced by electrochemical conversion technologies including heat pump technologies. These technologies offer the promise to be cheaper, moreefficient with no harmful emissions to the air, land, or water. A smart symbiosis between electricity and hydrogen as zero-carbon energy carriers with electrochemical and heat pump technologies, will establish a clean, costeffective, reliable, fair, and circular energy system.