Hydrogen has the potential to play an important role as a sustainable and environmentally acceptable source of energy in the 21st century. Present methods for producing hydrogen are mainly based on the reforming of fossil fuels with subsequent release of greenhouse gases. To avoid producing greenhouse gases, the possibility to use heat and surplus electricity from nuclear power plants to produce hydrogen by water cracking is being investigated. This report presents the state of the art in the nuclear production of hydrogen and describes the scientific and technical challenges associated with it.