In this thesis, the religious conversion process among the local population in the Western Rhodope, an area under the rule of the Ottoman Empire,is examined. The importance and location of the Rhodope during the expansion of the Ottoman Empire in the Balkans is evaluated and compared with the conquests of Bosnia and Albania and the initiation of the Islamization process, where the conversion to Islam took place differently in each of these 3 regions. Although the Ottoman Empire did not directly conqueror exert effort for Islamization in the Western Rhodopian region, the Pomaks residing in the region in the 15th century began to become Muslims, where such transition is clearly evidenced in the tahrir defters used in this thesisdated 1445, 1464/65 and 1478/9. Through these three defters, it is possible to have an insight into the processof Islamization in the Pomak settlement units, thus invalidating the theories on forced Islamization.