 Descriptive decision theory is concerned with characterising and explaining regularities in the choices that people are disposed to make. It is standardly distinguished from a parallel enterprise, normative decision theory, which seeks to provide an account of the choices that people ought to be disposed to make. Much of the work in this area has been devoted to the building and testing of formal models that aim to improve on the descriptive adequacy of a framework known as “Subjective Expected Utility” (SEU). This adequacy was first called into question in the middle of the last century and further challenged by a slew of experimental work in psychology and economics from the mid 1960s onwards.