“To write a book so that the people of our land…. [would] know the bond of Islam,” was the stated aim of Ahmed Yazıcıoğlu as he composed Envarü'l-Asıkin, a Turkish work of catechistics and dogmatics in the Ottoman frontier city of Gelibolu in 1451. Alongside his older brother Mehmed, the Yazıcıoğlus completed a widely-read set of vernacular writings on religion that helped define the popular face of Ottoman Sunnism. But why were they so keen on presenting a basic vision of Islam to the ordinary believer of Rumelia in the mid-fifteenth century? This article will explore how the Yazıcıoğlus' catechistic corpus emerged out of the interconfessional conversations of the Ottoman frontier lands. It is here argued that the Yazıcıoğlus' dogmatics can be read as attempts to clarify a perceived confusion as to the boundaries between Islam and Christianity, a synthesis that could teach an audience of new or unlettered Muslims the distinctness of their own religious community. This article invites further exploration of the way Ottoman imperial piety, just as in other early modern societies, continued to bear traces of its origin in the borderlands and its particular local circumstances.