An introduction to the main issues and research findings underlying decision-making and judgment under uncertainty. The focus is on the contrast between the normative theory of judgment and choice, and the psychological principles that guide decision behavior, often producing biases and errors. Among other topics, we will consider political, medical, and financial decision-making, poverty, negotiations, and the law, along with the implications of the findings for the rational agent model typically assumed in economics, throughout the social sciences, and in policy making.