Pré-publication, Document de travail: One of the greatest success stories in our societies is that people are living longer, life expectancy at birth being now above 80 years. Whereas the lengthening of life opens huge opportunities for individuals if extra years are spent in prosperity and good health, it is however often regarded as a source of problems for policy-makers. The goal of this paper is to examine the key policy challenges raised by increasing longevity. For that purpose, we first pay attention to the representation of individual preferences, and to the normative foundations of the economy, and, then, we consider the challenges raised for the design of the social security system, pension policies, preventive health policies, the provision of long term care, as well as for long-run economic growth.