We report the observation of coherent emission from three rare‐earth ions in electro‐optic crystals. Oscillation is observed from Nd3+ions in Bi4Ge3O12, LiNbO3, and Ba0.75Ca0.25Nb26O at room temperature, and from Tm3+and Ho3+ions in LiNbO3at 77°K. Second‐harmonic radiation is obtained from LiNbO3:Tm3+and electric‐field modulation of threshold is observed for certain crystals of LiNbO3:Nd3+. The latter effect is believed to arise from crystal strain. The propagation angle for phase‐matched second‐harmonic generation is calculated to lie at 43° to thecaxis for both LiNbO3:Tm3+and LiNbO3:Ho3+at 77°K. Phasematched second‐harmonic generation from LiNbO3:Nd3+is not possible, since the maser line is an extraordinary wave. However, the polarization of the maser line in LiNbO3:Nd3+is appropriate for phasematched parametric frequency conversion in the near infrared. Attempts to observe such radiation were not successful due to the limited power available in the fundamental.