What are the boundary zones between normal aging and Alzheimer's disease (AD)? Are many elderly people whom we regard as normal actually in the early stages of AD? Alzheimer's disease does not develop overnight; the early phases may last for years or even decades. Recently, clinical investigators have identified a transitional condition between normal aging and and very early Alzheimer's disease that they have called mild cognitive impairment, or MCI. This term typically refers to memory impairment beyond what one would expect in individuals of a given age whose other abilities to function in daily life are well preserved. Persons who meet the criteria for mild cognitive impairment have an increased risk of progressing to Alzheimer's disease in the near future. Though many questions about this condition and its underlying neuropathology remain open, full clinical trials are currently underway worldwide aimed at preventing the progression from MCI to Alzheimer's disease. This book addresses the spectrum of issues involved in mild cognitive impairment, and includes chapters on clinical studies, neuropsychology, neuroimaging, neuropathology, biological markers, diagnostic approaches, and treatment. It is intended for clinicians, researchers, and students interested in aging and cognition, among them neurologists, psychiatrists, geriatricians, clinical psychologists, and neuropsychologists.