The sixth volume of the Handbook is devoted to topics related to aging and dementia. The volume is introduced by two chapters dealing with age-related cognitive and neurobiological alterations in animals, including a detailed review of data obtained with transgenic and knockout technology. The next chapter reviews the cognitive changes associated with normal aging. The gamut of symptoms that occur in Alzheimer's disease (AD) are then described and analyzed, they include effects on attention, language, memory, non-verbal functions with emphasis on spatial abilities, olfaction and the motor system. The discussion of dementia syndromes is presented in two sections. The first concerns AD, which is discussed from the points of view of epidemiology, neuropathology and neurochemistry and concludes with a review of current and future treatments. The other section deals with non-AD dementias including Fronto-temporal and Lewy body dementias and specific conditions such as Parkinson's and Huntington's disease, as well as HIV infection. The volume includes a review of brain imaging and cerebral metabolism findings in aging and dementia. The final chapters review the relations between culture and dementia and the special syndrome of severe dementia.