Abstract In-situ superconducting YBCO thin films have been grown on (100)MgO substrates using RF planar magnetron sputtering from single, sintered, stoichiometric, targets. The films are c-axis oriented with Tc(onset) = 90 K and Tc(zero = 40–75 K. Processing variables and target characteristics strongly affect the composition and quality of these films. Control of variables such as substrate temperature, target-substrate orientation, oxygen and Argon partial pressures, target composition, target density, and target age is essential to achieve reproducibly the growth of high-quality superconducting thin films.