The link between sleep and aging is a hot topic of research. On the one hand, much attention has been paid to epidemiological studies showing that both short sleep and long sleep in humans are associated with reduced longevity. I will briefly review this literature and discuss recent experiments in the fruit fly Drosophila melanogaster that may contribute to understanding this complicated association. On the other hand, other experiments have focused on age-related sleep changes. Sleep quantity and quality tend to decrease with age, but the underlying mechanisms remain unclear. In young subjects, converging evidence from human and animal studies shows that the need for sleep is strongly modulated by the amount of brain plasticity during prior wake. In short, the more we learn and adapt our brain to an ever-changing environment, the more we need to sleep. If so, poor sleep in the elderly could be caused by a chronic decrease in sleep need due to reduced opportunity to learn and be exposed to novel experiences, rather than, or in addition to, an intrinsic problem in the neural circuits responsible for sleep regulation. This distinction has obvious practical implications. However, very little research has been done on this topic.