The book guides the reader from the foundations of statisti-§cal thermodynamics including the theory of intermolecular§forces to modern computer-aided applications in chemical en-§gineering and physical chemistry. The approach is new. The§foundations of quantum and statistical mechanics are presen-§ted in a simple way and their applications to the prediction§of fluid phase behavior of real systems are demonstrated. A§particular effort is made to introduce the reader to expli-§cit formulations of intermolecular interaction models and to§show how these models influence the properties of fluid sy-§stems. The established methods of statistical mechanics -§computer simulation, perturbation theory, and numerical in-§tegration - are discussed in a style appropriate for newcom-§ers and are extensively applied. Numerous worked examples§illustrate how practical calculations should be carried out.