Many surfaces and interfaces exhibit unique structural, chemical, and electronic properties, which have been exploited for many years (e.g. in catalysis) despite the lack of a thorough understanding. This has always required an intense research effort and special experimental tools, which were mainly developed in the second half of the last century. The availability of synchrotron radiation, in particular at a brilliant source such as the ESRF, has led to the development and routine exploitation of new, powerful experimental techniques for the analysis of surfaces and interfaces. The techniques available today permit studies that were impossible only a few years ago. Particularly the high penetration power and/or high momentum resolution permit the study of surfaces and interfaces under real conditions and on a wide range of length scales. The experimental studies highlighted in the following should give a taste of the activities at the ESRF in the field of surface and interface science. 

While ultra-high vacuum (UHV) is still an important pre-requisite for surface science, researchers are nowadays concentrating increasingly on the study of "real" surfaces, i.e. surfaces in contact with gases or liquids. Two examples are reported here. The X-ray investigation of liquid/vapour interfaces at ID10B gave new insight into the structure and surface energy of such common interfaces. Trying to "observe" the growth of a crystal in situ, on an atomic scale has been a long standing desire. At ID32, X-ray scattering was used to analyse the growth from solutions of ADP (ammonium-dihydrogen phosphate) crystals, which are important for laser applications.

Whenever surfaces need to be studied "undisturbed", in situ analysis in UHV is required. This work is mostly carried out at the "classical" surface science beamlines ID3 and ID32, and we present three examples. The first case is an example from the steadily growing field of soft-condensed matter on surfaces. This study of methanethiol on a copper surface also demonstrates the particular strength of combining the X-ray standing-wave technique with photoelectron spectroscopy, allowing the structural characterisation of individual chemical species. In the second case, illustrated pictorially by X-ray scattering is the stunning influence of a surfactant (wetting layer) on the surface morphology of silver during its homoepitaxial growth. The third case documents the increasing interest in oxides and their surfaces. This is driven by scientific curiosity since traditional analysis tools often cannot be applied (e.g. to insulators) but also because of the fascinating associated phenomena such as high-temperature superconductivity and giant magnetoresistance and applications in sensor technology and catalysis etc. Both of these beamlines and BM32 were used to carry out a diffraction analysis of a surface reconstruction of the rock-salt oxide NiO.

The final two examples are right on the borderline between surface and interface science and applied materials science. Nanoscience, the whole field of which is strongly driven by imminent applications in information technology, is nowadays very fashionable and self-organisation has become an important concept. The X-ray analysis of such generated quantum dots, coined "nanotomography" by the authors, was carried out at ID15B and yielded a previously unavailable insight into these tiny objects. In the final example, the structural aspects of the industrially important surface hardening of steel by the introduction of nitrogen ("nitriding") were studied at BM29 by X-ray absorption spectroscopy.