The outline of the CALPHAD method, which has been developed to alleviate the difficulty in obtaining phase diagrams by experiments alone, is presented. This method enables calculation of stable and metastable phase equilibria, as well as thermodynamic properties such as activity, enthalpy, driving force, and so on. Some examples of the calculated phase diagrams, obtained by applying the CALPHAD method are reviewed, in connection with the design of their microstructures.