This textbook deals with the theoretical basis of chemical equilibria and chemical changes and emphasizes the properties of phase diagrams. The author treats the field from a modern perspective. He takes into account the dramatic changes in the methods of applying thermodynamics caused by the development both of computer operated 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 modeling are also given, and the book contains many exercises and worked solutions. This modern text will be of value to undergraduate and graduate students in materials science and chemistry.