This paper examines the process of composition of some of the most enduring and characteristic products of fifteenth-century Ottoman popular intellectual life: the vernacular oeuvre of the brothers Mehmed and Ahmed Yazıcızade (Bican), written between 1449 and 1466 in Gelibolu. The most famous of their works is the Muhammediyye, a poem written as a pious history “from Creation to Judgment Day”. Close behind in popularity is the Envarü'l-'Aşıkin, a prose rendition of the same content, as well as the Dürr-i Meknun and Kitabü'l-münteha, which are, respectively, a complex encyclopedic work and an expansive Turkish commentary on the theoretical Sufism of Ibn 'Arabi. In this study I explore the Yazıcızades' sources and methods. They faced the unenviable task of attempting to write comprehensive summations of Islamic religious knowledge and practice in a novel Turkish expression, while having at their disposal the limited intellectual resources of their frontier region. Accordingly, the two brothers worked cooperatively: the older Mehmed often wrote in Arabic, abridging and interpreting his modest library of Arabic and Persian source-texts, while the younger Ahmed translated these into a simple Turkish, adding elements of contemporary interest of his own. The resulting corpus involves adaptive translations from a particular body of Arabic and Persian classics, the incorporation of certain local oral histories, as well as the continuous refinement of this material in response to political circumstances, including the conquest of Constantinople. This is synthesized in such a way as to reflect a particular early Ottoman mentality – a concern with the boundaries between Islam and Christianity, a focus on the upright lives of the prophets that is matched by a fascination with the wonders and marvels of distant lands, an obsession with the imminence of war and apocalypse, and an ambivalent regard for the Ottoman state.