The rare-earth (R)-transition metal (M) compounds are of great interest for technical uses as permanent magnets, magnetostrictive and magnetic storage devices, magnetocaloric materials or hydrogen storage. In these systems, the magnetic behaviour of M components is the main factor in their technical applications. These cover the situation when transition metals are strong or weak ferromagnets or show an exchange enhanced magnetic susceptibility. Starting from experimental data and band structure calculations we analyse the formation of a magnetic ordered M moments, their evolution as function of composition and structure types, the 4f-3d exchange interactions as well as temperature induced moments. The evolution with pressure of transition metal moments in systems which show strong ferromagnetism as RCo5 compounds or weak ferromagnetism as in R-Co-B or RCo2 systems is discussed. As example, an ordered cobalt moment is present if the exchange field acting on a corresponding atom is higher than 75 T. Finally, some models are developed in order to explain the experimental data.