We use a cross-section of 59 countries to examine the impact of state religion and of constitutional protection of religion on the degree of religiosity within a country. Our measure of religiosity is the percentage of the population who attend religious services at least once a week. We find that both establishment of a state religion and constitutional protection of religion have significant (and opposing) effects. The existence of a state religion reduces attendance b y 14.6-16.7%o f the total population, where as each decade of constitutional protection increases attendance b y approximately 1.2% of the population. We also find that other measures of religious regulation have significant negative effects on attendance. Ironically, the motive behind establishment of a particular state religion usually is to strengthen that religion, but the effects are ultimately to undermine the vitality of the established religion.