Abstract. Countries differ in their religiosity and these differences have been found to moderate numerous psychological effects. The burgeoning research in this area creates a demand for a country-level religiosity index that is comparable across a large number of countries. Here, we offer such an index, which covers 166 countries and rests on representative data from 1,619,300 participants of the Gallup World Poll. Moreover, we validate the novel index, use it to examine temporal change in worldwide religiosity over the last decade, and present a comprehensive analysis of country-level religiosity’s nomological network. The main results are as follows. First, the index was found to be a valid index of global religiosity. Second, country-level religiosity modestly increased between 2006 and 2011 and modestly decreased between 2011 and 2017 – demonstrating a curvilinear pattern. Finally, nomological network analysis revealed three things: it buttressed past evidence that religious countries are economically less developed; it clarified inconsistencies in the literature on the health status of inhabitants from religious countries, suggesting that their psychological and physical health tends to be particularly good once economic development is accounted for; and finally, it shed initial light on the associations between country-level religiosity and various psychological dimensions of culture (i.e., Hofstede’s cultural dimensions and country-level Big Five traits). These associations revealed that religious countries are primarily characterized by high levels of communion (i.e., collectivism and agreeableness). We are optimistic that the newly presented country-level religiosity index can satisfy the fast-growing demand for an accurate and comprehensive global religiosity index.