Perturbation theory forms an important basis for predicting the thermodynamic characteristics of real fluids and solids. The first book entirely devoted to an extensive review of perturbation theories for the equilibrium thermodynamic properties of classical systems, this volume discusses theories developed in the context of density functional theories (DPT) and those used to deal with polyatomic molecular fluids, such as the statistical associating fluid theory (SAFT). With a focus on practical applications, the author provides guidance on how to use the many variations and applications of perturbation procedures to obtain the thermodynamic and structural properties of fluids and solids.