The fast globalization of the second half of the 20th century and the advent of new demographic and migratory trends have awakened the social sciences to the growing complexity of regional cultural dynamics. Social scientists have begun to associate cultural diversity with modernity, predicting it as an inescapable and perennial condition of modern societies that affects, and is affected by, religious phenomena. However, few systematic, indepth empirical researches have been made to assess these assertions. Thus, our paper puts forward the formulation of a diversity index (independent variable) based on four dimensions -linguistic, ethnic, religious, and place of birth- that is correlated with a (dependent) variable of individual religiosity. We conclude that, for the set of European countries and for the time period under analysis (1999-2014), theories of cultural diversity that link diversity to the displacement and recomposition of religiosity have no empirical validity.