Ferromagnetic and paramagnetic resonance has been observed in single crystals of EuS. A standard microwave spectrometer, operating near 22 Gc/sec, was used to measure the power absorption at 1.4 and 300°K. The resonance line width, 75 Oe at 1.4°K, was found to be approximately 1200 Oe at room temperature. An upper limit of 30 Oe has been established for the magnitude of the magnetocrystalline anisotropy field, in contrast to the value of - 190 Oe found for EuO. The paramagnetic line width is explained solely on the basis of spin-spin interactions. The anisotropy results are understood in terms of crystal-field perturbations of the magnetic Eu2+ ion. © 1965 The American Physical Society.