Abstract: Water consists of H and O atoms. It is most important to find an efficient and economic method to dissociate H2O to obtain H2. The adsorption of H2O on solid surfaces is commonly observed, and on the surfaces of certain metals or metal oxides the adsorbed H2O can be dissociated. This paper presents some results on the adsorption and dissociation of H2O on MgO (100) films and Pd/MgO (100) surfaces investigated under ultrahigh vacuum conditions by using photoemission spectroscopy and high resolution electron energy loss spectroscopy. The results indicate that H2O can be partially dissociated on the MgO (100) surface at initial coverages, while the dissociation of H2O on Pd/MgO (100) surfaces is Pd coverage dependent. More fundamental research is needed to understand the mechanism of interaction of water with solid surfaces.