From the reign of Bayezid II (r. 1481-1512) onwards the persecution of Anatolian Qizilbash, varying in degree and intensity, seems to run like a red thread through the history of the Ottoman Empire until well into the seventeenth century. Imperial fermans to provincial administrators ordering the execution of everybody with the “stain” of having Qizilbash tendencies and of actually being Qizilbash were common phenomena by the time of Süleyman the Magnificent (r. 1520-1566), while the persecution of the Qizilbash often appears to have amounted to well-planned massacres. Perhaps the most significant persecution, however, seems to have happened under Selim I (r. 1512-1520) before the campaign that culminated in the Battle of Çaldiran (1514), when Selim’s order to his clerks to record the names of all Qizilbash sympathizers “between seven and seventy years of age” into defters was followed by their imprisonment or their execution by the sword. Why was the persecution of so many Qizilbash in Anatolia ordered? The simple answer, according to Ottoman chroniclers, is that Selim I wanted to avoid any possibility of resistance and revolt during his expedition against Shah Ismail, especially since he was aware of the extent of the Safavid influence in Anatolia, as exemplified by the Shahqulu Rebellion in 1511. There is little doubt, however, that the severity of the Ottoman response to the Qizilbash threat was related to something more than strategic military concerns. In my presentation, I will focus on the Ottoman response to the Shahqulu Rebellion and emphasize that it was in the aftermath of this particular rebellion that the Ottomans began to perceive the Qizilbash as the most significant threat to their social and religious order and initiated proactive and preemptive policies against the spread of Shi‘i Islam, in turn establishing the boundaries of an Ottoman understanding of Sunni Islam.