The chapter deals with the hybridization of the Catholic community of Izmir during the late 17th and early 18th centuries that led the emergence of the Levantine group as a new social and cultural actor in the city. The first part of the chapter is dedicated to the detection of how the term Levantine has been used, both historically and by historiography, whereas the second focuses on the Catholic missionaries of Izmir, their Levantinizing practices and the non-endogamic attitude of Izmir’s Catholic parishioners. The missionaries’ responses to interreligious coexistence is described as a process of adaptation that favoured orthopraxy (the ethical ‘right action’) in respect to the orthodoxy (the doctrinal ‘right belief’) and promoted the comunicatio in sacris. The interaction between the missionaries and their Catholic parishioners (i.e. between Levantinized practices and proto Levantines’ behaviours) highlights the emergence of a new hybridized mentality, the actual agent that – along with interreligious marriages – forms the basis of the ‘historical’ Levantine identity. The original sources for this chapter are again the letter of the missionaries to Propaganda Fide between 1683 and 1724.