One of the basic questions concerning religious pluralism in societies is whether it has a reinforcing or an undermining effect on religiosity of individuals. The two contradicting hypotheses are on the one hand the ‘market theory’ on the other hand the ‘secularization theory’. According to the ‘market theory’ a vast supply of religions in society also increases the demand for it and thus reinforces the religious vitality. The ‘secularization theory’ states that individual religiosity is weakened by a plurality of religions in society. The study presented in this video tests both theories empirically for the United States of America and for Western Germany using data covering more than fifty years. As DETLEF POLLACK explains, the findings confirm the secularization theory for both societies. This might indicate a positive relation between modernization and secularization that so far is doubted by many researchers.