The clinician's experience of dementia and mild cognitive impairment suggests that these conditions are present in a variety of forms and progress at different rates. This new work begins by asking the question 'what is normal in cognitive and pathological aging?' It uses diagnostic imaging, histopathological findings, schematic diagrams, and other graphics to illustrate the symptom profiles, etiology, and epidemiology of the more common dementias. The authors present comparisons of Alzheimer's and Lewy body diseases, frontal temporal and vascular dementias and other dementing illnesses, to illustrate the problems inherent in distinguishing between them, and in making a diagnosis.