Although being a classic discipline, phase diagram studies have lost nothing of their importance in modem materials science. On the contrary, the study of phase equilibria becomes even more important as materials development plays an increasing key role in the realization of new technologies, due to the fact that the materials systems on which such technologies are based become more complex and consist of an increasing number of components. In this paper, progress in the methodology of phase equilibria studies is discussed. Moreover, typical examples of applied phase diagram research are presented, which show how an intimate understanding of microstructural development, as well as the optimization of property values and the combination of certain material properties can be developed from the knowledge of phase equilibria.