This book has three aims. The first is to describe to scientists interested in basic biogerontology a panel of available model organisms where the aging process has been well-studied and where (with the exclusion of man) external interventions have been proven capable of extending life span. The second aim of the book is to emphasize the commonalities among experimental manipulations that are able to confer life extension across species. The third aim of the book is to offer objective and reasonable speculations in the science of life span extension to scientists of diverse background and to physicians. The scope of the book will be broad. Model systems ranging form unicellular organisms to man will be examined. However, the overall context of the discussion will be the common mechanisms relating aging and longevity that have been identified in each system These common mechanisms will provide the unifying feature for the discussion and will provide the reader with an understanding of the possible links between aging and longevity that have been uncovered in the past decade.