Aging is the progressive decline in biological functions over time. This decline targets macromolecules, cells, tissues and, as a consequence, whole organisms. Despite considerable progress in the development of testable hypothesis concerning aging in an evolutionary context, a unifying theory of the molecular/physiological mechanistic causes of aging has not been reached. In fact, is it not clear to what extent aging is a programmed or stochastic process. This book takes the reader from unicellular bacterial deterioration via senescence in yeast and worms to aging in rodents and humans, allowing a comparative view on similarities and differences in different genetic model systems. The different model systems are