This chapter focuses on the central question: what is the role of Greek thinking in the development of Christianity? This question is shaped by a judgment about how profoundly the revolutionary Greek texts of incipient Christianity were influenced by the Greek language and culture in which they were produced. The chapter explores three key moments in the history of Catholic engagement with the philology of Hellenization. The first is Guillaume Budé’s De transitu Hellenismi ad Christianismum, written amid the religious violence and intense arguments of the Reformation. The second is Festugière’s Observations stylistiques sur l’Évangile de Saint Jean: this is explored in relation to nineteenth- and early twentieth-century arguments about how Greek philosophy added a distorting corruption to Christianity. Third is the Regensburg Address, delivered by Pope Benedict XVI in 2006. Recalled mainly for its apparent attack on Islam, the text is more remarkable for its reversal of centuries of Catholic theology about Hellenization.