In recent years, there has been considerable interest in oxyhydrides in both materials science and physics due to their Mott insulating behaviour , superconductivity and mixed electronicionic conduction . The favorable electron and hydride ion transport properties together with the low mass of hydride ions and high electrode potential of the H 2 /H redox couple ( 2.3 V) make these materials particularly attractive for developing energy storage devices with high energy density. Since the synthesis of the first oxyhydride several tens of new structures have been prepared and characterized. Among these the most extensively investigated which exhibit some of the most interesting chemicophysical properties are the perovskite-structured ATiO 3 x H y (A = Ca, Sr, Ba) materials. BaTiO 3 x H y has been shown to incorporate high hydride ion concentrations up to y = 0.6, moreover, and has demonstrated high electric and hydride ion conductivity. Complete understanding of the electron and hydride ion transport mechanisms and their relation to the oxyhydride composition is crucial for rational design of materials with specifically tailored characteristics.