The Brown Boveri Scientific Symposia by now are part of a firmly established tradition. This is the tenth event in a series which was initiated shortly after Corporate Research was created as a separate entity in our company; the symposia are held every other year. The themes have been: 1969 Flow Research on Blading 1971 Real-Time Control of Electric Power Systems 1973 High-Temperature Materials in Gas Turbines 1975 Nonemissive Electrooptic Displays 1977 Current Interruption in High-Voltage Networks 1979 Surges in High-Voltage Networks 1981 Semiconductor Devices for Power Conditioning 1983 Corrosion in Power Generating Equipment 1985 Computer Systems for Process Control 1987 Process Technologies for Water Treatment The tenth event in an uninterrupted series that by now goes back almost 20 years is a good opportunity to make a few remarks on the guiding rules that have governed our symposia. Why have we chosen these titles? At the outset we establislwd certain selection criteria; we felt that a subject for a symposium should fulfill the following three requirements: It should characterize a part of an established discipline; in other words, it should describe an area of scholarly study and research. It should be of current interest in the sense that important results have recently been obtained and considerable research is still being undertaken in the world's scientific community. It should bear some relation to the scientific and technological activity of the company.