Our objective in this introductory chapter is, first, to briefly trace the history of observations, research, and ideas that have led to the differentiation between implicit and explicit memory and to the current intense investigation of this domain. The emphasis is on the contributions from each of the three areas that are represented in the separate parts of this book: cognitive psychology, develop­ mental psychology, and neuropsychology. Our second goal is to discuss what makes the study of implicit and explicit memory important and exciting, and to justify why we chose to focus this book on three particular research domains.