This chapter explains uniform oscillations of magnetization in an anisotropic ferromagnet magnetized to saturation. It also explains general methods of allowance for the influence of anisotropy on ferromagnetic resonance and investigates, using these methods, the most important case of magnetocrystalline anisotropy. The exchange interaction of spins, in the absence of orbital moments, is isotropic. Therefore, the magnetocrystalline anisotropy can be caused either by other interactions of spins or by the spin–orbital interaction. The exchange interaction, which is anisotropic in the presence of spin–orbital coupling, influences the ionic energy levels and determines, together with the crystal field, their angular dependence. The measurement of anisotropy constants by ‘static’ methods, i.e., at small rates of the change of magnetization direction, yields these renormalized constants. But if the rate of magnetization change is high enough, e.g., at ferromagnetic resonance, the measurement of anisotropy constants gives another values of anisotropy contants.