Since the first edition, the research literature on aging continues to expand rapidly, reflecting both the rising interest of the scientific community and also the needs of a growing older population. In the year 1900, persons over 65 years of age were the smallest portion of developed societies. Today they are emerging as the largest. Aging is a complex process of change involving influences of a biological, behavioral, social, and environmental nature, all of which are explored in the context of this encyclopedia. The second edition includes all new articles and wholly new coverage of topics that have seen research advances. It is also available online via ScienceDirect (2006) featuring extensive browsing, searching, and internal cross-referencing between articles in the work, plus dynamic linking to journal articles and abstract databases, making navigation flexible and easy. Organized alphabetically by article title, this work consolidates and summarizes pertinent findings while providing additional readings. Breadth of coverage spans biology, psychology, social science, health science, and humanities. Every article contains a definition paragraph and a glossary of unfamiliar terms. It is fully cross-referenced and contains a complete subject index.