Background: France has been among the first countries to become secularized but has preserved a Catholic identity. Before 2008, French laws made it very difficult to collect data on an individual’s religious affiliation. The dataset "Enquête Mode de Vie des Français" is the first allowing one to collect such data.

Objective: I investigate the impact that being a Catholic has on fertility in France. I answer two main questions: (i) Do Catholic people have more children than others? (ii) Why is this the case?

Methods: Fertility is measured by the number of children ever born. I use the dataset "Enquête Mode de Vie des Français" and Zero-Inflated Poisson regression models. Individual religiosity is approximated by the attendance at religious services.

Results: I first show that practicing Catholics have more children than the rest of the population, while this is not verified for nominal Catholics. I also construct two variables allowing me to detect that particularized ideology mechanisms (Goldscheider 1971) can explain in part why religion has an impact on fertility in my dataset. Nevertheless, I cannot exclude the social interaction hypothesis. The multivariate analysis I provide also validates the main mechanisms of the rational actor model.

Conclusions: I implement several robustness checks showing that my main results are robust to changing my regression model (ordered probit and linear regressions) and the way religiousness and fertility are measured.