This volume is a collection of the lectures presented at the NATO Advanced Study Institute "Interfacial Aspects of Phase Trans­ formations", held in Erice (Sicily) in 198t. The Institute was the seventh course of the International School of Crystallography, es­ tablished in the Center of Scientific Culture "Ettore Majorana" in 1974, with the guidance and inspiration of L. Riva di Sanseverino and A. Zichichi. The course organizers, R. Kern and myself, were advised and helped in developing the program, and in the choice of lecturers and participants, by R.F. Sekerka, F. Bedarida, J.L. Katz and J. G. Dash. Although the scope of the Institute (as reflected in the content of this book)