Hydrogen storage materials research is entered a new and exciting period with the advent of the nanocrystalline alloys. A review is given on the basic properties of nanocrystalline TiFe, ZrV₂, LaNi₅ and Mg₂Ni phases. First, the mechanical alloying process used for manufacturing these hydrides is described and the crystallographic and thermodynamic properties are detailed. Then the electrochemical behaviour of nanocrystalline hydrogen storage compounds in conditions of their performance in rechargeable nickel hydride (Ni-MH_x) batteries is given. Finally, the electronic properties of nanocrystalline alloys are presented.