Autophagy, a lysosomal process involved in the maintenance of cellular homeostasis, is responsible for the turnover of long-lived proteins and organelles that are either damaged or functionally redundant. The process is tightly controlled by the insulin-amino acid-mammalian target of the rapamycin-dependent signal-transduction pathway. Research in the last decade has indicated not only that autophagy provides cells with oxidizable substrate when nutrients become scarce but also that it can provide protection against aging and a number of pathologies such as cancer, neurodegeneration, cardiac disease, diabetes, and infections.