Ferromagnetic resonance measurements have been performed on single‐crystal samples of the hexagonal ferrites BaFe12O19, Zn2Y, and Co2Y. Values of linewidth,gvalue, and anisotropy field are given as a function of temperature from 77°K to 600°K at various frequencies between 8 and 75 kMc. Zn2Y is singularly interesting because it exhibits an extremely narrow room temperature linewidth atXband. Values as low as 16 oe, with anisotropy fields of 9000 oe are reported. The theory of the resonance behavoir is developed and compared to the experimental results.