This thesis presents some investigations into a variety of paramagnetic systems. Electron paramagnetic resonance is often used to investigate the behaviour of paramagnetic ions present as substitutional impurities in diamagnetic host crystals. Measurements have been carried out at liquid helium temperatures on single crystals of aluminium acetylacetonate doped to 2% with ruthenium 3+ ions. The spectrum at nitrogen temperatures has been reported by Jarrett (1957) who found two ruthenium sites.