Abstract
We review equilibrium thermodynamic properties of systems of magnetic particles like ferrofluids in which dipolar interactions play an important role. The review is focused on two phenomena: (i) magnetization with the initial magnetic susceptibility as a special case and (ii) the phase transition behaviour. Here, the condensation ('gas/liquid') transition in the subsystem of the suspended particles is treated as well as the isotropic/ferromagnetic transition to a state with spontaneously generated long-range magnetic order.