Health professionals and the public are increasingly concerned with the dimensions of health and health care affecting adults as they age: diseases that impact aging adults; their health care, quality of care and their ability to access it; and the psychosocial, biological, and historical dimensions of health and health care. The need for accurate and up-to-date information is particularly acute as older adults assume an increasing proportion of the population of the United States.The opening chapters of this Encyclopedia cover the history and demography of aging, the biology of aging, cultural diversity, legal aspects, and more. The second portion offers encyclopedic entries on topics related to the health of older adults. Each entry includes a listing of suggested readings and suggested resources, in print and online.The Encyclopedia is accessible both to professionals and to the lay public. The information presented will be of value to clinicians and researchers who work with adults age 50 and over, and to those who wish to increase their understanding of the aging process.