The variation of the viscosity of aqueous and non-aqueous electrolyte solutions with salt concentration has been studied and the results interpreted in terms of a number of mathematical models. The effects of ion-association on the viscosity of electrolyte solutions has been investigated by measuring the viscosity of aqueous solutions of some thallous salts. The viscosities of alkali halide salts in formamide have been determined over a range of temperatures and new methods for the division of viscosity B-coefficients into ionic contributions have been proposed. The results of these studies have been interpreted in terms of the ion-solvent interactions. The intermolecular interactions present in binary liquid mixtures of formamide with methanol, ethanol propan-l-ol and butan-l-ol have been studied by viscosity measurements over the complete concentration range. Finally the usefulness of time domain dielectric spectroscopy in solute-solvent interaction studies has been briefly investigated.