Age-related loss of memory and other cognitive abilities has been recognized since antiquity. However, the need to understand the causes and consequences of dementia has become urgent over the past quarter-century because of the large and increasing proportion of persons in the world's population who live into their 9th and 10th decades -- the ages at which people are at greatest risk for dementia. Dementia is now one of the most common and feared conditions of old age and is a major public health problem throughout the world. The condition demands more than a basic understanding on the part of nearly all health care professionals. Dementia is the second edition of a multiauthored book on the subject. The book has 70 chapters organized in 7 sections. About a third of the book is devoted to general aspects of dementia, a quarter to Alzheimer's disease, and the rest to vascular dementia, dementia with Lewy bodies, focal dementia (e.g., Pick's disease and progressive aphasia), dementia associated with neuropsychiatric disorders (e.g., depression, schizophrenia, alcoholism, and Huntington's disease), and other types of dementia (e.g., dementia in Creutzfeldt-Jakob disease and in human immunodeficiency virus infection). The book does not represent the American view of dementia: only 18 authors from 10 U.S. institutions are included among the 132 authors.