A hydrogen storage composition has a hydrogenated state and a dehydrogenated state; in the hydrogenated state the composition comprises a metallic hydride having a metallic component which reversibly forms the hydride and a metallic heat transfer medium in intimate contact with the hydride which transfers heat to the hydride for dehydrogenation; in use hydrogen is liberated from the composition with transfer of heat to the heat transfer medium, the hydrogenated state may be regenerated by exposing the composition in a dehydrogenated state to hydrogen gas. In this way a source of hydrogen gas is provided which source may be regenerated.