Thermodynamics is an essential tool used today for analysis and design by process simulation. The chapter describes generalised computational methods and thermodynamic modelling. The network of thermodynamic relations makes possible to navigate between different properties, mostly not accessible by measurements, only on the basis of limited experimental information. The general conditions of chemical and phase equilibrium are presented. A distinct section is devoted to the equations of state, particularly of cubic type with predictive capabilities, as well as to new methods based on molecular modelling. The final section describes methods for generating charts and tables for various properties.