This book collects together selected papers presented at the Second Interna- tional Conference on the Structure of Surfaces (ICSOS-II). The conference was held at the Royal Thopical Institute in Amsterdam, The Netherlands, June 22-25, 1987. It was held in part to celebrate the 25th anniversary of the NEVAC (Netherlands Vacuum Society). The International Organizing Committee members were: M. A. Van Hove (Chairman) J. F. van der Veen (Vice-Chairman) W. F. van der Weg (Treasurer) D. L. Adams A. M. Bradshaw M. J. Cardillo D. J. Chadi J. E. Demuth J. Eckert G. Ertl S. Ino D. A. King B. I. Lundqvist J. B. Pendry Y. Petroff J. R. Smith G. A. Somorjai J. Stohr S. Y. Tong X. D. Xie The ICSOS meetings serve to assess the status of surface structure determination and the relationship between surface or interface structures and physical or chemical properties of interest. The papers in this book cover: theoretical and experimental structural techniques; structural aspects of metal and semiconductor surfaces, including relaxations and reconstruc- tions, as well as adsorbates and epitaxial layers; phase transitions in two dimensions, roughening and surface melting; defects, disorder and surface morphology. Amsterdam, Berkeley J. F. van der Veen October 1987 M. A. Van Hove v Acknow ledgements We wish to acknowledge the many organizations and individuals whose contributions made possible the Second International Conference on the Structure of Surfaces and these Proceedings.