The ferromagnetic Curie temperature of EuO films has been increased by selective doping with trivalent rare-earth oxides. The electrical resistivity, which depends upon the temperature and has a broad peak at ≈100°K, decreases markedly to ≈10-1 Ω·cm with doping. A typical ferromagnetic Curie temperature, determined from magneto-optic measurements in zero applied field, is ∼135°K. Maximum longitudinal Faraday rotation occurs at 0.65 μ with a specific rotation of +1×105 deg/cm for an incidence angle of 20 deg. At 0.84 μ the Faraday rotation reverses sign and reaches a negative maximum at 0.93 μ. The longitudinal Kerr rotation also has two maxima at 0.58 μ and 0.83 μ with double rotations of ≈4°. The transverse Kerr effect depends on the wavelength in the same manner and has maximum values of +0.4 and -0.3, respectively. There is a strong optical absorption band centered at 0.6 μ (at 300°K) with α≈1.2×105 cm-1 which shifts toward longer wavelengths at lower temperatures accompanied by a small decrease in α. An additional absorption band centered around 0.4 μ with amplitude less than 10% of the main absorption peak appears as a result of doping. Quasistatic switching measurements show that the coercive force depends strongly upon the stress in films arising from the difference in thermal expansion coefficients of EuO and substrates. Hc is typically 120 and 60 Oe on fused quartz and 0080 glass, respectively, with remanence of ∼0.7. Results of the transport, magnetic, magneto-optical, and optical properties are discussed in terms of indirect exchange via conduction electrons. © 1968 The American Institute of Physics.