The object of this work was to provide accurate experimental values of the primary thermodynamic excess functions - the excess Gibbs energy G^E, the enthalpy of mixing HE, and the excess volume V^E - of suitably chosen binary liquid mixtures, with which modern theories of solutions, especially those which take polarity into account, could be tested. All the systems studied, therefore, involve at least one (multi-)polar component, this being selected from the following substances: HCl,N₂O, C₂H₄ , CH₄ , CF₄ and C₂F₆. Xenon was used as the second, non-polar component in four of the binary mixtures. G^E was derived from vapour pressure measurements, HE determined by calorimetry, and V^E ob- tained by a pyknometric technique. The experimental results obtained for each of the excess properties, M^E, where generally fitted to a Redlich-Kister-type equation.