Mg-based alloys are promising hydrogen storage materials because of the high gravimetric energy density of MgH2 (7.6 wt.%). A majordisadvantage, however, is its very slow desorption kinetics. It has been argued that, in contrast to the well-known rutile-structured Mg hydride,hydrided Mg-transition metal alloys have a much more open crystal structure facilitating faster hydrogen transport. In this paper, the electrochemicalaspects of new Mg–Sc and Mg–Ti materials will be reviewed. Storage capacities as high as 6.5 wt.% hydrogen have been reached with veryfavourable discharge kinetics. A theoretical description of hydrogen storage materials has also been developed by our group. A new lattice gasmodel is presented and successfully applied to simulate the thermodynamic properties of various hydride-forming materials. The simulation resultsare expressed by parameters corresponding to several energy contributions, for example mutual atomic hydrogen interaction energies. A good fitof the lattice gas model to the experimental data is found in all cases.