Decision theory is the study of how agents make choices under uncertainty, values, objectives, and beliefs. It includes normative approaches that prescribe rational decision-making and descriptive approaches that analyze how decisions are actually made.
(Also theory of choice.) The study of the reasoning underlying an agent's choices. Decision theory can be broken into two branches: normative decision theory, which gives advice on how to make the best decisions given a set of uncertain beliefs and a set of values, and descriptive decision theory which analyzes how existing, possibly irrational agents actually make decisions.