This paper analyses the evolution of the French pension system from the mid-nineteenth century to the current period. Competing or complementary hypotheses that can explain the long-run rise in pension expenditure are discussed. The determinants that appear to offer the best explanation for the evolution of pension expenditure are economic growth, the process of industrialization and ageing. The time series related to these determinants are cointegrated over the long run. A multivariate model is estimated in order to assess the long-run elasticities between the pension expenditure and its main determinants.