ABSTRACT. For centuries people have speculated on how to improve decision making without much professional help in developing clarity of action. Over the last several decades, many important contributions have been integrated to create the discipline of decision analysis, which can aid decision makers in all fields of endeavor: business, engineering, medicine, law, and personal life. Because uncertainty is the most important feature to consider in making decisions, the ability to represent knowledge in terms of probability, to see how to combine this knowledge with preferences in a reasoned way, to treat very large and complex decision problems using modern computation, and to avoid common errors of thought have combined to produce insights heretofore unobtainable. The limitation to its practice lies in our willingness to use reason, rather than in any shortcoming of the field. This chapter discusses the sources of the discipline; the qualities desired in a decision process; the logic for finding the best course of action; the process of focusing attention on important issues in attaining clarity of action; the need for clear and powerful distinctions to guide our thinking (because most decisions derive from thought and conversation rather than from computation); and the challenges to the growth of the discipline.