The effect of oxygen vacancies on the electronic and magnetic properties of La 0.66 Sr 0.33 Mn O 3 (LSMO) has been investigated by means of ab initio calculations within the density-functional formalism combined with photoemission. The simulations show that the introduction of oxygen vacancies causes a shift of the valence-band features toward higher binding energies and an increase of the degree of covalency of Mn bondings. The Mn magnetic moments undergo some changes, keeping, however, the situation relatively close to the ideal nondefective system: in none of the different vacancy configurations, a drastic charge or spin rearrangement occurs. There is, though, an important vacancy-induced drawback: half-metallicity, typical of the perfectly stoichiometric system, is generally lost due to defective bands that cross the Fermi level. Photoemission experiments performed on epitaxial thin films of LSMO with …