In this chapter, it is shown that DISQUAC is a useful tool to describe phase diagrams (vapour–liquid, solid–liquid and liquid–liquid equilibria). Special attention is paid to the fact that DISQUAC is a mean field theory with a critical exponent for the order parameter equal to 0.5. Concentration–concentration structure factors [S_CC(0)] and Kirkwood–Buff integrals (G_ij) have been determined, using DISQUAC, for a number of mixtures of the type 1-alkanol or polar compound + heptane or 1-alkanol + polar compound. It is found that 1-alkanol + di-n-propyl ether (DPE) or + dimethyl carbonate (DMC) or + ethanenitrile (EtN) systems are characterized by homocoordination. In DPE solutions, this is mainly due to the alcohol self-association. Homocoordination in systems with DMC or EtN arises from dipolar interactions between like molecules. 1-Alkanol + tertiary amide mixtures are characterized by heterocoordination, i.e. by interactions between unlike molecules. Discussion of the results is conducted not only in terms of S_CC(0) and G_ij values, but also taking into account different thermophysical properties (liquid–liquid equilibria, calorimetric data) and models. This procedure should be considered as a standard method, needed to obtain conclusions of greater soundness.