Abstract
The Electron Paramagnetic Resonance (EPR) technique is described as a valuable tool in order to probe the spin correlations in π-radical magnets. The peculiar features of the EPR response of low dimensional exchange coupled spin systems are recalled. The extreme sensitivity of the resonance field to both magnetic and dipolar interactions is emphasized. The example materials include phthalocyanine radical derivatives and nitronyl nitroxide radical derivatives. Both exhibit either anti ferromagnetic or ferromagnetic intermolecular interactions.