High quality superconducting films of YBa₂Cu₃O_7−x were deposited in situ using single target 90° off-axis sputtering. We have investigated their superconducting DC and RF properties, their normal state properties, and their microstructures. These films are distinctly different from bulk crystals and post-deposition annealed films. Sharp superconducting transition temperatures can be reproducibly obtained by control of deposition parameters. The T_c can be varied from 75 to 89 K. The optimization of properties other than T_c and the control of film texture occur under conditions different from those for which the highest T_c is obtained. Normal state conductivities are as high as or higher than those of single crystals. Critical current densities reach 6 × 10⁷ A/cm² at 4.2 K. All the above properties are relatively insensitive to compositional variations. The T_c's have a much weaker dependence on the c-axis lattice parameters than do those of bulk samples. The measured low-temperature penetration depth is 1400 Å and surface resistance at 4.2 K and 10 GHz is as low as 16 μΩ. Microstructural studies show sharp interfaces between films and their substrates and a variety of defect structures. Many of the properties of in situ films can be explained by clean grain boundaries and the characteristics of the surface growth occuring during in situ deposition.