Islam in Bulgaria is a minority religion and the second largest religion in the country after Christianity. According to the 2021 Census, the total number of Muslims in Bulgaria stood at 638,708 corresponding to 9.8% of the population. According to a 2017 estimate, Muslims make up 15% of the population. Ethnically, Muslims in Bulgaria are Turks, Bulgarians and Roma, living mainly in parts of northeastern Bulgaria (mainly in Razgrad, Targovishte, Shumen and Silistra Provinces) and in the Rhodope Mountains (mainly in Kardzhali Province and Smolyan Province). History The first documented Muslim contacts with Bulgaria are dated to the mid-ninth century when there were Islamic missionaries in Bulgaria, evidenced by a letter from Pope Nicholas to Boris of Bulgaria that the Saracens must be extirpated. During the time of Tsar Simeon insignificant Islamic influences on Bulgarian art began to appear, though it is believed that these can be traced to Byzantine influence. Later during the 11th and 12th centuries, nomadic Turkic tribes such as the Cumans and the Pechenegs entered Bulgaria and engaged the Byzantine Empire. According to scholars, some of these were Muslim. Migration of Muslim Seljuq Turks to Dobruja during the 13th century is also mentioned. In 1392, the Ottoman Empire conquered the Second Bulgarian Empire. Bulgaria remained under Ottoman and Islamic rule for almost five centuries, but Christians in Bulgaria retained their culture and status, first as dhimmis and later as equals under the millet system, though until their liberation they were called giaour, meaning "infidel" as an offensive term. Muslim population in Bulgaria was a combination of indigenous converts to Islam, and Muslims originating outside the Balkans. According to scholarly consensus, conversion to Islam was voluntary as it offered Bulgarians religious and economic benefits. Missionary activities of the dervish orders resulted in mass conversions to Islam; though many converts retained Christian practices such as baptism, celebration of Christian holidays etc. Most of the urban areas became Muslim majority, whereas the rural areas remained overwhelmingly Christian. Following the Russo-Turkish War and the 1878 Treaty of Berlin, the Danube Vilayet of the Ottoman Empire was transformed into the autonomous Principality of Bulgaria. The Muslim population of the Danube Vilayet prior to the war numbered 1,120,000. This principality was expanded after the First Balkan War when largely-Muslim Rhodope and Western Thrace regions were incorporated into the country's territory. This process was accompanied by forced Christianization of Muslim Pomak settlements. These