Why did religiosity decrease in the Western World during the twentieth century? Raphaël Franck * Laurence R. Iannaccone ** Abstract This article analyzes the decline in religiosity in the Western World during the twentieth century by using long-run data on church attendance. It tests the secularization hypothesis, which argues that economic growth decreases religiosity, and the religion- market model, which considers that governmental interventions in religious affairs have an impact on religiosity. The results provide scant evidence for the secularization hypothesis. They however support the religion-market model by showing that the growth of the welfare state significantly diminished religiosity. Such findings therefore suggest that many individuals were historically observant because churches offered welfare services which were not provided by the State. Keywords: Church Attendance, Economic Growth, Religiosity, Secularization, Welfare State. JEL Classification: H53, N32, N34, Z12. * Bar Ilan University, Department of Economics, 52900 Ramat Gan, Israel. Tel: +972-3-531-8935. Fax: +972-3-738-4034. Email: franckr@mail.biu.ac.il ** Chapman University, Argyros School of Business and Economics, Orange, CA, USA. Tel: +1-714 744- 7007. Fax: 1+714-532-6081. Larry@EconZone.com . Raphaël Franck gratefully acknowledges financial support of the Adar Foundation of the Economics Department at Bar Ilan University.