During the past fifteen years there has been a dramatic increase in the number of different surfaces whose structures have been determined experimentally. For example, whereas in 1979 there were only 25 recorded adsorption structures, to date there are more than 250. This volume is therefore a timely review of the state-of-the-art in this dynamic field.

Chapter one contains a compilation of the structural data base on surfaces within a series of tables that allows direct comparison of structural parameters for related systems. Experimental structural trends amongst both clean surfaces and adsorbate systems are highlighted and discussed.

The next chapter outlines the successes of local density functional theory in predicting the relaxations and reconstructions of clean metal and semiconductor surfaces, and the behaviour of adsorbates such as hydrogen, oxygen and alkali elements on metal surfaces, thereby explaining some of the experimental trends observed within the database. These "ab initio" density functional calculations are of ground state properties at the absolute zero of temperature.

Chapter three provides an introduction to finite temperature effects in a pedagogical review of current statistical mechanical treatments of phase transitions at surfaces, many of which display the prominent role of fluctuations or non-mean field behaviour.

The final chapter discusses the relationship of the reactivity of a surface to its morphology and composition, which is particularly relevant to a fundamental understanding of catalysis.

Surface crystallography is a discipline which has come of age. There exist in the literature several hundred complete determinations of atomic configurations at surfaces: yet the number is not so great that cataloguing these structures is too daunting a task. We felt that now was the right moment to begin a compilation that could be updated at frequent intervals to give a comprehensive picture of the known surface world. The following pages are the product of our labours. Our target community is the large number of surface chemists, materials scientists, physicists and others whose work involves surfaces. As the compilation expands with time our hope is that it will become one of the standard reference works for structures: in the manner that Wyckoff and other X-ray tables are for bulk crystals. We have devoted considerable thought to the format. The system we have chosen will no doubt have its critics, and in subsequent editions may well be improved, but it has been arrived at after extensive consultation. A problem that we faced in putting structures into standard format was the diversity of conventions used in the literature. It is to be hoped that our system will have sufficient virtue to serve as a standard format for future reporting of structures. That would make it much easier for surface crystallographers to use the work of others.