In recent years, there has been a massive upsurge in interest in the psychology of thinking and reasoning. This book contains contributions from virtually all the main players involved in research into these areas. It focuses on three reasoning problems devised by Peter Wason which have inspired countless journal articles over the past 25 years: the selection task, the 2-4-6 task and the THOG problem. Despite this intense interest, the reasons why people make so many errors in these seemingly simple tasks are still not fully understood. A variety of different theoretical perspectives have been used in trying to explain performance. These include: the mental models approach, the pragmatic reasoning approach and the mental logic approach. All of the leading proponents of these theories have contributed chapters to this book in which they expand and update their theories. Other chapters, some reviewing the literature, others offering new theoretical perspectives, have been produced by leading researchers from both sides of the Atlantic. There is a final chapter from Peter Wason himself, whose early research prompted the initial interest in these areas. He describes how he came to create the tasks which have proved so influential. The entire book is in essence a tribute to his enormous contribution to research in the psychology of reasoning. This book will be of relevance to all those interested in human thinking, including students and researchers in psychology, cognitive science and philosophy.