The authors present superconducting YBa2C3O7 (YBCO) thin films grown in-situ by three-ion-beam sputtering. Y, Y2O3, Cu, Cu2O, BaF2 and BaCO3 sputter targets have been investigated. The highest quality films were prepared using a BaCo3 target. Auger analysis of films grown using a BaCO3 target show no carbon content. Y2O3 and Cu2O are more suitable than the native metals as sputter targets for YBCO growth as they are much less prone to sputter rate variations with oxygen partial pressure. They also supply oxygen to the growing film. As-deposited YBCO films are metallic (resistivity 240 μΩ cm at 100 K), reflective, and of highly homogeneous composition with Tco transition temperatures of 73 K and transition widths of 15 K. Post-annealing in flowing oxygen improves TCO's to 82 K. Critical currents are in excess of 105 A cm-2 at 77 K. Films are textured with c-axis orientation perpendicular to the (100) SrTiO3 substrate surface. As-deposited superconducting YBCO films have also been prepared on SiO2 and Y2O3 buffer layers on Si wafers