During the last two centuries the potential of electronic data processing (EDP) has been used to an increasing degree to support human decision making in different ways. In the sixties the management informations systems (MIS) created probably exaggerated hopes of managers. Since the late 1970s and early 1980s decision support systems (DSS) found their way into management and engineering: The youngest child of these developments are the so-called Knowledge-based expert systems or short expert systems. If one interpretes decisions rather general, that is, including evaluation, diagnosis, prediction, et cetera, then all three types could be classified as decision support systems which differ gradually with respect to the following properties: 1. Does the system “optimize” or just provide information? 2. Is it generally usable or just for specific purposes and areas? 3. Is it self-contained with respect to procedures and algorithms or does it “learn” and “derive” inference and decision making rules from knowledge which is inquired from a human (expert) and analysed within the system?