In this paper a theory for magnetic relaxation phenomena developed in the framework of thermodynamics of irreversible processes (TIP) with internal variables by G. A. Kluitenberg (G.A.K.) and the author is reviewed. Analogies and correlations with thermodynamic theories with internal variables for mechanical distortional phenomena and dielectric relaxation phenomena, derived, respectively, by G. A. K., and by G. A. K. and the author, following the same procedure, are put forward as evidence. It is assumed that if n different types of irreversible microscopic phenomena give rise to magnetic relaxation, it is possible to describe these microscopic phenomena splitting the total specific magnetization in n + 1 parts and introducing n of these partial specific magnetizations as internal variables in the thermodynamic state space. The phenomenological equations are formulated in the anisotropic and isotropic cases. Finally, linearizing the equations of state, generalizations of the Snoek equation for magnetic relaxation phenomena are obtained by eliminating the internal variables. Some results obtained in the paper are new.