This textbook conveys the methods suitable for making decisions in various areas of life, such as economics, politics, medicine, or personal matters, with a higher degree of rationality. Key focuses include decisions in the face of conflicting goals, decisions under risk, decisions with incomplete information about one's own preferences or probabilities, as well as considerations of time preferences and decision-making in committees. Particular emphasis is placed on the applicability of the procedures. A number of concrete application examples demonstrate the value of the methods for a wide range of decision-making problems. Through realistic exercises, the reader is facilitated in acquiring the methods of decision theory.