This book is a collection of selected papers presented at the First Interna- ti onal Conference on the Structure of Surfaces (ICSOS-1). ICSOS-1 was hel d on the Berkeley campus of the University of California during August 13-16, 1984. The International Organizing Committee members were: S.Y. Tong (Chairman), M.A. Van Hove (Vice-Chairman), D.A. King (Secretary), D.J. Chadi (Treasurer), D.L. Adams, A.M. Bradshaw, M.J. Cardillo, J.E. Demuth, J. Eckert, G. Ertl, B.I. Lundqvist, J.B. Pendry, Y. Petroff, M. Simonetta, J.R. Smith, G.A. Somorjai, J. Stohr, R. Ueda, and X.D. Xie. The series of ICSOS meetings was initiated to assess the status of surface- structural determi nati on and the rel ati onshi p between surface or interface structures and physical or chemical properties of interest. The subject mat- ter includes solid and adsorbate-covered surfaces, well-established and promising new surface-sensitive techniques, and results of experimental and theoretical studies. The physical and chemical properties of a surface or interface are often critically determined by its atomic-scale structure. A variety of techniques has been developed to study this structure and its connection with the sur- face or interface properties of single crystals and of imperfect and amor- phous interfaces. The papers in this book cover the theory of surface structure, new analy- tical techniques for surface structure, new developments in established structural techni ques, recent structural resul ts, defect structures, and phase transitions at surfaces.