This book contains the papers presented at the international symposium Polycrys- talline Semiconductors - Grain Boundaries and Interfaces (POLYSE '88) that was held in Malente, FRG, from August 29 to September 2, 1988. This conference has two roots: Firstly, it is a successor to a conference on polycrystalline semi- conductors held in Perpignan, France, in 1982 and to a summer school in Erice, Italy, in 1984. Secondly, it continues a series of German workshops on polycrys- talline semiconductors, which have been organized every year since 1983 by two of the present editors (H. P. S. and J. H. W. ) in Stuttgart, FRG. As in these previ- ous workshops, the symposium POLYSE '88 also tried to bridge the gap between fundamental research and technological aspects of polycrystalline semiconductors with emphasis on physical properties. In order to realize this conception, 12 scientists recognized in their fields were invited to give reviews of their respective work. The expert presentations of these scientists complemented by all other contributions, including an ad hoc evening workshop on the chemical analysis of grain boundaries by scanning tunneling microscopy, resulted in a lively and rewarding symposium. We would particularly like to thank the invited speakers for their talks, as well as for undertaking the task of refereeing the submitted papers. These speakers are: L. N. Aleksandrov Y. Ishida P. Pirouz A. Bourret J. D. Joannopoulos H. W. Schock H. Cerva L. L. Kazmerski H. Teichler F. Greuter S. Martinuzzi K. N.