Perturbation theory forms an important basis for predicting the thermodynamic characteristics of real fluids and solids. This book provides a comprehensive review of current perturbation theories-as well as integral equation theories and density functional theories-for the equilibrium thermodynamic and structural properties of classical systems. Emphasizing practical applications, the book avoids complex theoretical derivations as much as possible. Appropriate for experienced researchers as well as postgraduate students, the text presents a wide-ranging yet detailed view and provides a useful guide to the application of the theories described.