The low-lying valence levels of BeO, are calculated by the LCAO MO SCF method in order to ascertain the nature of the ground state of the molecule. Calculations of excited states using virtual orbitals are found to be inconclusive. Better results are found by doing variational calculations on three low-lying configurations for a series of internuclear distances, employing a large basis set and data on differences in molecular correlation energies between the various configurations. The calculations indicate a closed-shell 1Σ+ ground state. Spectroscopic constants are derived for this and other valence states. An unobserved 3Σ+—3Π transition is predicted to lie in the infrared region at about 9000 Å. The lowest-lying excited state is a 3Π. This level is shown to lie sufficiently high with respect to the ground state so as not to require an alteration of the published dissociation energy.