Many studies in cognitive psychology have provided evidence of systematic deviations in cognitive task performance relative to that dictated by optimality, rationality, or coherency. The texts in this volume present an account of research into the cognitive biases observed on various tasks: reasoning, categorization, evaluation, and probabilistic and confidence judgments.The authors have attempted to discern the contribution of the study of bias to our understanding of the cognitive processes involved in each case, rather than proposing an inventory of the different types of biases. A special section has been devoted to studies on the correction of biases and cognitive aids.