© 2022 Ankara Haci Bayram Veli University. All rights reserved.The issue of Islamic differentiation in Anatolia is probably the most attractive subject of Islamic history of Anatolia. This subject, on which researchers have spent a lot of time since Fuad Köprülü, has been studied mostly through the representatives of differentiation, distinctive features and the origins. The debates on the concepts preferred to characterize the difference are still alive. As a researcher who deals with almost every aspect of the subject and produces works, Ahmet Yaşar Ocak is in the position of addressing almost all these discussions. Ocak creates also a typology of Islamic differentiation while dealing with the subject through both mystical and ulama representatives. He conceptualizes the Qalandarīs, whom he treats as representatives of the profession, as marginal ṣūfīsm while evaluating the Malāmīs, Hamzavīs, Gulshanīs and some individual representatives from the ulama within the scope of heresy and atheism, with its own terminology of the Ottoman period. As the basis of this characterization, he highlights the non-Islamic and customary attitudes and even social deviance for Qalandarīs, and non-Islamic behaviours for Malāmīs, and also extreme pantheism almost common to all. Ocak also deals with the issue of where these distinctive features originate from, both through the influence of pre-Islamic beliefs and with their extensions in the Islamic period and within the framework of new formations over time.