The invention relates to a process and a plant for producing hydrogen by steam reforming and high-temperature electrolysis. Steam reforming produces a synthesis gas from a carbon-containing starting material and steam. Process heat generated in the context of the steam reforming is utilized for producing steam from water. Thus-produced steam is utilized as reactant for producing an electrolysis product in a high-temperature electrolysis step, wherein the electrolysis product includes at least hydrogen and oxygen. Hydrogen is separated from the synthesis gas produced by steam reforming and from the electrolysis product produced by high-temperature electrolysis.