The book deals with decision-making situations where multiple decision criteria must be considered. The decision problems may either involve fewer countable decision alternatives or have a continuous solution space. These problems are examined from both the formal decision-theoretical perspective and the pragmatic side of decision support. It addresses both well-defined decision situations and poorly structured environments. The book has emerged from a lecture held over several years at RWTH Aachen and is intended as a textbook. Each chapter includes relevant key references, making it easier for students to access the pertinent literature. The authors pay special attention to the didactic structure.