The Hagia Sophias of Istanbul, Iznik, and Trabzon shared similar conversion histories. All three were built as Byzantine churches, converted into mosques under the rule of the Ottoman Empire, and functioned as museums in the 20th century. Transforming such emotionally charged spaces, either into buildings reserved for the practices of another religion or into public museums open for visitation, requires major physical and conceptual changes, which are closely related to the political, historical and social contexts in which they take place, and are deeply embedded in long-term contestation over these sites. In this talk, Professor Tanyeri-Erdemir focuses on the debates around the museumification and de-museumification of these emotionally charged buildings, analyzing the historical, political, social, religious, and institutional factors in the manifestation of major structural and conceptual changes related to the museumification and de-museumification practices.