Studies of the yeast Saccharomyces cerevisiae reveal four processes determining life span: metabolism, stress resistance, chromatin-dependent gene regulation, and genome stability. The retrograde response, which signals mitochondrial dysfunction resulting in changes in nuclear gene expression, extends yeast life span and is induced during normal aging. This response involves extensive metabolic adaptations. The retrograde response links metabolism and genome stability during yeast aging. A reduction in the availability of nutrients also extends yeast life span. This metabolic mechanism operates by pathways distinct from the retrograde response, although it shares with the latter some longevity effectors. Life extension by calorie restriction entails re-modeling of mitochondrial function. The retrograde response appears to compensate for age changes, while calorie restriction may be a preventive mechanism. The maintenance of age asymmetry between the mother and daughter yeast cells also depends on mitochondrial function. Loss of this age asymmetry occurs during normal yeast aging and may be a paradigm for stem cell aging. The importance of mitochondrial integrity in yeast longevity is emphasized by the role of prohibition function in attenuating oxidative damage. Our studies point to the central role of mitochondria in yeast aging. They highlight the importance of the maintenance of mitochondrial membrane potential, which drives the transport of biosynthetic precursors derived from the Krebs cycle. Common threads weave their way through the studies of aging in yeast and in other model organisms. This suggests conserved features of aging across phyla.