Many scholars have noted the remarkably diverse and fluid religious scene of the frontier regions in Anatolia within which the Ottomans emerged. as one of many Turco-Muslim principalities committed to ghaza, or holy war. Islam as a proselytizing religion in the early Ottoman milieu was comparatively more tolerant and embracive, represented by an assortment of Sufi orders and itinerant dervish groups, as well as the more orthodox-minded ulema. Sectarian boundaries were porous and adaptable, with mainstream Sunnism showing a relative receptivity to Shi‘i/Alid influences. In fact, it has been argued that the hallmark of the early Ottoman religious milieu was “metadoxy” defined as “a state of being beyond doxies, a combination of being doxy-naïve and not being doxy-minded.” However, the transformation of the Ottoman regime from a ghazi principality to one with an imperial vision in tandem with its emerging claim to the leadership of the Sunni-Muslim world (following its annexation of the Mamluk territories, including the two holy cities, Mecca and Medina, and its defeat of the Shi‘i Safavids) affected a gradual change of the Ottoman religious milieu from the “metadoxy” of the earlier centuries to the strident sectarianism of the 16th Century. A pivotal figure in this process was the famous sixteenth-century Ottoman sheikh ul-Islam, Ebussu‘ud, who is best-known for his synthesis of dynastic and religious law. This paper will argue that Ebussu‘ud, through his thousands of fatwas that were issued on a wide variety of topics, was in effect defining, and spelling out the boundaries of, Islamic orthodoxy, and thereby (re)inventing what might be called “Ottoman Sunnism.” What was distinct about this new Sunni synthesis? What were the ideological and material dynamics that played into its making? What were its fault lines and internal tensions? How successful was the state in enforcing this new orthodoxy? These are the questions that the proposed paper will address.