AbstractBACKGROUNDFrance 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 Enquete Mode de Vie des Francais is the first allowing one to collect such data.OBJECTIVEI 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?METHODSFertility is measured by the number of children ever born. I use the dataset Enquete Mode de Vie des Francais and Zero-Inflated Poisson regression models. Individual religiosity is approximated by the attendance at religious services.RESULTSI 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.CONCLUSIONSI 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.1. IntroductionDemographers have initiated a long tradition that consists in studying the relationship between religion and fertility. To do so, they have constructed a framework in which alternative theories compete and complete each other. The present paper is a contribution to this literature, and focuses on contemporary France. More precisely, it studies the impact that being a Catholic has on fertility, measured either by the number of children ever born, or by completed fertility.Due to its limitation to France, this study is characterized by several specificities. First, despite its Catholic identity, France is very secularized (Hervieu-Leger 2004) and it was the first European country to become secular. Lesthaeghe and Wilson (1986) argue that early secularization in France has been one major reason why the French fertility transition has been concomitant with the mortality transition.2 This explains why the population did not explode during the demographic transition. Since 1945, the proportion of churchgoing Catholics has kept decreasing dramatically. This process accelerated during the seventies. Hervieu-Leger (2004) estimates that in 2001, the proportion of French people who engage in at least one element of Catholic practice3 per month was about 12%. Interestingly enough, despite this early and strong secularization, fertility in France is among the highest in Europe.4 As shown in Figure 1, the total fertility rate in France decreased from the beginning of the 20th century to the nineties; then it increased and has almost reached the replacement level.5Second, until 2008, French laws made it very difficult to collect data on an individual's religious affiliation. As a consequence, results about the relationship between religion and fertility are lacking for France. If religion had no impact on fertility, this specificity would not weaken the analysis of individual fertility behavior, but in line with the literature, this paper shows that this is not actually the case.The data set Enquete Mode de Vie des Francais contains data about religion and several dimensions of the respondents' religiousness, as well as complete information about their economic situation (income, savings, wealth, history on the labor market, etc.), their lifestyle (health, addictions, consumer habits, etc.), their risk aversion and their values (religion, politics, attitude toward foreigners, etc. …