This textbook deals with the theoretical basis of chemical equilibria and chemical changes and emphasises the properties of phase diagrams. A feature of the book is the author's treatment of the field from a modern perspective, taking into account the dramatic changes in the methods of applying thermodynamics caused by the development both of computer programs for sophisticated equilibrium calculations, and of extensive databases containing thermodynamic parameter values for individual phases from which all thermodynamic properties may be calculated. This new situation has inspired a new approach to the teaching of basic thermodynamics. Illustrative examples of thermodynamic modelling are also given, and the book contains many exercises and worked solutions. This modern text will be a useful supplement to traditional thermodynamics texts for advanced undergraduate and graduate students in materials science and chemistry.