Potential curves for the ground and various excited states of the MgO molecule have been calculated using the multi-reference configuration interaction (MRD CI) method. The electronic structure of the states is analyzed in terms of their semi-diffuse, ionic, Rydberg, and valence character and the electric dipole moments of the low-lying states are given. Special emphasis is placed upon the ionic-covalent interactions which give rise to numerous avoided crossings, primarily at large internuclear separations. The character of the low-lying 1Σ + states which have distinct multiconfigurational nature is carefully investigated.