The relaxation processes move a system to the state of thermodynamical equilibrium. If the forces that had removed it from this state stopped their action, the relaxation processes bring the system to equilibrium. The relaxation processes now perform the steady energy flow from the modes excited by external forces and determine dissipative parameters of system for forced oscillations, i.e., the anti-Hermitian parts of the sucseptibility tensor components. In most cases energy is transferred finally to the lattice that results in heating it (i.e., in the creation of phonons, in terms of corpuscular theory). Therefore, all relaxation processes that result in the flow of energy from the magnetic system are called often spin–lattice processes. The concepts of spin–spin and spin–lattice relaxations were introduced first in the theory of paramagnetic relaxation. In particular, in magnetically ordered substances, as distinct from paramagnets, relaxation rates of longitudinal and transverse magnetization components are nearly same and are determined by both the spin–spin and spin–lattice processes.