The effect of some simple salts on the viscosity of formamide has been studied at a number of temperatures and interpreted in terms of ion-solvent interactions using the equation suggested by Jones and Dole. Further evidence to support the various conclusions drawn has been provided by application of Eyring's reaction rate theory to the viscosity processes in solution. The viscosities of binary mixtures of formamide and water, methanol or dimethylformamide have been investigated over the whole composition range and the ability of three semi-empirical models to describe these systems has been discussed. A new three parameter equation has been proposed. Finally the effect of sodium chloride on the binary mixture formamide/water has been considered. It has been shown that, in general, for viscosity measurements to be a useful tool for investigating ion-solvent and solvent-solvent interactions, it is important that the measurements be made at more than one temperature.