Up until now, the budding research on the nature of Ottoman Sunnitization (or Sunnification) has suggested in a rather unambiguous manner that starting in the early sixteenth century—brought on by the rising religio-political challenge of Shi’a Safavids as well as certain internal developments in the Ottoman realms—and stretching all the way through the seventeenth century, Ottoman political and religious elites, but also common people, put considerable effort into defining, defending and enforcing a Sunni orthodoxy and orthopraxy. However, this process did not take place in isolation from religio-political developments in other contemporary religious communities, both in the Ottoman Empire and beyond. Rather, as I argue, the Ottoman experience of Sunnitization was part of a broader “age of confessionalization” that affected both Europe and parts of the Middle East, including the Ottoman Empire. The paper will delve into the arena of Ottoman confessionalization, of which the articulation of a Sunni orthodoxy and orthopraxy was one aspect. It will provide some preliminary evidence on the dialogic dimension of this phenomenon, namely on how in certain parts of the Ottoman Empire—in this case Ottoman Rumeli—Catholic, Protestant, and Sunni Muslim confessionalizing initiatives met, grappled and potentially influenced each other in terms of strategies and genres of confessionalization. At the heart of the paper will be the catechetical literature, the Sunni Muslim ilm-i hals in Ottoman Turkish as well as catechisms in the vernaculars (often in translation from Latin) circulated in the borderlands between the Ottomans and the Venetians and the Ottomans and Habsburgs in the sixteenth and early seventeenth centuries.