On the basis of an original survey among native Christians and Muslims of Turkish and Moroccan origin in Germany, France, the Netherlands, Belgium, Austria and Sweden, this paper investigates four research questions comparing native Christians to Muslim immigrants: (1) the extent of religious fundamentalism; (2) its socio-economic determinants; (3) whether it can be distinguished from other indicators of religiosity; and (4) its relationship to hostility towards out-groups (homosexuals, Jews, the West, and Muslims). The results indicate that religious fundamentalist attitudes are much more widespread among Sunnite Muslims than among native Christians, even after controlling for the different demographic and socio-economic compositions of these groups. Alevite Muslims from Turkey, by contrast, show low levels of fundamentalism, comparable to Christians. Among both Christians and Muslims, strong religiosity as such is not (among Christians) or only mildly (among Muslims) related to hostility towards out-groups. Fundamentalist believers, however, show very high levels of out-group hostility, especially among Muslims.