This article focuses on conversion in Ottoman Middle East and its social dimension. Since religion was a key element in shaping the social hierarchies in the Ottoman reality, conversion to Islam was a way to cross communitarian boundaries and improve social status. Converting meant, first of all, changing religious community with all the administrative and legal consequences implied. As has been shown, conversion to Catholicism also guarantees to the convert an improvement of his/her socio-economic conditions. More problematic is whether it implies a change of religious community. Reconstructing the spread of the Catholic faith in Bethlem (17th century), through a wide range of sources - Registers of conversion drown up by the Franciscan friars, local Christian chronicles, travel accounts, Ottoman fiscal surveys - will shed a light on conversion to Catholicism in the 17th century and its particular features.