Dissociative chemisorption of H2O at the MgO(100)-water interface has been investigated both experimentally and theoretically. Ln particular, metastable impact electron spectroscopy (MIES) was used to image the density of occupied states on the MgO(100)/Mo(100) surface for various degrees of water exposure. After multilayer water desorption, spectral features typical of surface hydroxyls are present. To further study the possibility of dissociative chemisorption of water, a theoretical and computational method called CECILIA (combined embedded cluster at the interface with liquid approach) was used to calculate the geometry, energetics, and electronic density of states (DOS) for interfacial species. Consistent with experiment, our theoretical results predict that dissociative adsorption of H2O at the MgO(100)-water interface is energetically more favorable than molecular adsorption. The stabilization of charged OH- and H+ interface adsorbates is due to polarization of the surrounding solvent.