The Brown Boveri Symposia are by now part of firmly established tradition. This is the seventh event in a series which was initiated shortly afer Corporate Research was established as a separate entity within our Company; the Symposia are held every other year. The themes to date 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 Why have we chosen these titles? At the outset we established certain selection criteria; we felt that a subject for a Symposium should fulfill the following require ments: It should characterize a part of a thoroughly scientific 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 effort is underway in the international scientific community. It should bear some relation to the scientific and technological acitivity of our Company. Let us look at the requirement "current interest": Some of the topics on the list have been the subject of research for several decades, some even from the beginning of the century. One might wonder, then, why such fields could be regarded as particularly timely in the 1960s and 1970s. A few remarks on this subject therefore are in order.