Process for the production of hydrogen by the thermochemical route from water, based on the chlorine/cerium cycle, in which, according to a first reaction scheme, the following reactions are carried out: H.sub.2O+Cl.sub.2=2HCl+1/2O.sub.2; (A) 8HCl+2CeO.sub.2=2CeCl.sub.3+Cl.sub.2+4H.sub.2O; (B) 2CeCl.sub.3+4H.sub.2O=2CeO.sub.2+6HCl+H.sub.2; (C) or in which, according to a second reaction scheme, the following reactions are carried out: H.sub.2O+Cl.sub.2=2HCl+1/2O.sub.2; (A) 8HCl+2CeO.sub.2=2CeCl.sub.3+Cl.sub.2+4H.sub.2O; (B) 2CeCl.sub.3+2H.sub.2O=2CeOCl+4HCl; (B') 2CeOCl+2H.sub.2O=2CeO.sub.2+2HCl+H.sub.2; (C') and in which the reaction (B) for the chlorination of cerium oxide is carried out in the liquid phase, the cerium chloride passing into solution.