The last few years have ~een rapid improvements in semiconductor growth techniques which have produced an expanding range of high quality heterostructures for new semiconductor devises. As the dimensions of such structures approach the nanometer level, it becomes increasingly important to characterise materials properties such as composition uniformity, strain, interface sharpness and roughness and the nature of defects, as well as their influence on electrical and optical properties. Much of this information is being obtained by electron microscopy and this is also an area of rapid progress. There have been advances for thin film studies across a wide range of techniques, including, for example, convergent beam electron diffraction, X-ray and electron energy loss microanalysis and high spatial resolution cathodoluminescence as well as by conventional and high resolution methods. Important develop­ ments have also occurred in the study of surfaces and film growth phenomena by both microscopy and diffraction techniques. With these developments in mind, an application was made to the NATO Science Committee in late summer 1987 to fund an Advanced Research Work­ shop to review the electron microscopy of advanced semiconductors. This was subsequently accepted for the 1988 programme and became the "NATO Advanced Research Workshop on the Evaluation of Advanced Semiconductor Materials by Electron Microscopy". The Workshop took place in the pleasant and intimate surroundings of Wills Hall, Bristol, UK, during the week 11-17 September 1988 and was attended by fifty-five participants from fourteen countries.