Since the first introduction of MCI, research interest has grown exponentially, and the utility of the concept has been investigated from a variety of perspectives in different populations of interest (e.g., clinical samples, volunteers, population-based screening) in many different countries. Much variability in findings has resulted. Although it has been acknowledged that the differences observed between samples may be ‘legitimate variations’, there has been no attempt to understand what it is we have learned about MCI (i.e., common features and differences) from each of these perspectives. This book brings together information about MCI in different populations from around the world. will be an important resource for any clinician, researcher, or student involved in the study, detection, treatment, and rehabilitation of people with MCI.