Should GDP be replaced by a single measurement of well-being? Some people think so, arguing that an improvement in the quality of life is more important to people than the mere promotion of growth. Without going quite as far as this radical stance, increasing numbers of policymakers as well as the American Central Bank and the European Union feel that indicators of well-being should be built alongside GDP. Quality of life covers several dimensions. Some of them are qualified as objective, such as material situation, physical health, emotional balance and social isolation, while others are more subjective, such as satisfaction with life. New longitudinal data provide a quantification of the concepts underlying well-being and a longer-term understanding of how the different dimensions of quality of life interact with each other. The one that people consider the most important is the weakness of social ties, ahead of health and psychosocial risks. Knowledge of the importance of these different dimensions to each person may be helpful in building a single quality-of-life indicator. But it is debatable whether the publication of a single figure would be of interest, since this figure gives no information on the best economic policy measures intended to improve it. It is probably far better to know about the populations in difficulty, to pinpoint those that combine several causes of poor quality of life, and to propose targeted measures to increase their dynamic capabilities, as described by Sen, in order ultimately to improve their situation.