Tne entry of a solute into a solvent will affect the interactions between solvent molecules by making, breaking, strengthening or weakening solvent-solvent bonds. In a binary mixed solvent the relative partial molar entropies, si, and excess entropies of mixing, ASE, are related to these interactions. Thus a relationship between the entropy of transfer, A S P , of a solute and these thermodynamic parameters might be expected. A general relationship is developed and successfully applied to the A S P for alkali-metal halides in methanol-water mixtures. The results of this analysis show that, for this system at least, A S P is dominated by the effects of changes in solvent-solvent interactions, in contrast to the enthalpy of transfer, AH?. Combination of the results of this analysis with those previously reported for AH? allows a complete, quantitative explanation of the thermodynamics of solvation in the alkali-metal halides in methanol-water mixtures.Recently' we showed that the enthalpies of transfer, AH?, of a solute in a mixed solvent could be related, quantitatively, to changes in the enthalpies of solvent-solvent bonding in the mixed solvent. This model was found to account satisfactorily for AH? of simple electrolytes in methanol-water mixtures, where they pass through broad maxima as functions of solvent composition, and in acetonitrile-water mixtures, where the (AH?, x,) profiles show sharp minima.In this paper we derive an analogous relationship for the entropy of transfer, ASP, and apply this to data for the alkali-metal halides in methanol-water systems. The variations in the ASP data with solvent composition largely result from the changes in solvent-solvent bonding.The results of this analysis are combined with those from the analysis of the corresponding AH? data and show that the treatment represents satisfactorily the free energies of transfer, AGP.