This textbook provides a thorough introduction to normative and descriptive decision theory. It is aimed at students of economics, lecturers, and practitioners who want to acquire the tools for solving decision problems. Building on the general foundations for the representation and resolution of decision problems, decision problems under risk are analyzed in an application-oriented manner. Issues related to the evaluation of uncertain outcomes, the processing and assessment of information, and the sharing of risks are addressed, as well as decisions made in groups. Three chapters are also dedicated to the foundation of financial corporate objectives and the derivation of compatible decision criteria. In the 10th, updated, and expanded edition, all chapters have been supplemented with summaries of the topics covered.