A new approach to understanding irrational behavior that provides a framework for deriving new models of human cognition What does it mean to act rationally? Mathematicians, economists, and statisticians have argued that a rational actor chooses actions that maximize their expected utility. And yet people routinely act in ways that violate this prescription. Our limited time and computational resources mean that it is often unrealistic to consider all options in order to choose the one that has the greatest utility. This book suggests a different approach to understanding irrational behavior: resource-rational analysis. By reframing questions of rational action in terms of how we should make the best use of our limited resources, the book offers a new take on fundamental questions at the heart of cognitive psychology, behavioral economics, and the design of artificial intelligence systems. The book presents a formal framework for applying resource-rational analysis to understand and improve human behavior, a set of tools developed by the authors to make this easier, and examples of how they have used this approach to revisit classic questions about human cognition, pose new ones, and enhance human rationality. The book will be a valuable resource for psychologists, economists, and philosophers as well as neuroscientists studying human brains and minds and computer scientists working to reproduce such systems in machines.