It's estimated that almost half of Bulgaria's population was massacred or enslaved and transported to another part of the empire within a few years of the Turkish conquest, whose long-term effects were equally profound. The Ottoman Empire not only isolated Bulgaria from the European Renaissance, but imposed and maintained a harsher system of feudalism than had previously existed. Muslim colonists occupied the most fertile land and prosperous towns, while the surviving Bulgarians - mainly peasants - became serfs of the Turkish Spahis (land-holding knights), who gouged them for their own profit and for numerous state taxes. In northern Bulgaria and the Rhodopes some Bulgarians succumbed to forced Islamicization and, as converts ( pomaks ), gained rights denied to the Christian Rayah or "Herd", notably exemption from the hated blood tax or devshirme , whereby the oldest boys were taken from their families and indoctrinated before joining the elite Ottoman janissary corps.

The Turks looted monasteries and subordinated the native Orthodox Church to the Patriarchate of Constantinople, which imposed Greek bishops and ignorant, grasping clergy on the faithful. Worst of all was the perpetual insecurity, for Bulgarians were raped and robbed by Turkish troops or "visiting" dignitaries, cheated by tax collectors and Greek merchants, and had no way of getting justice through the Ottoman courts.

Ottoman power in Bulgaria was repeatedly challenged by popular rebellions , which tended to break out whenever Turkish armies were beaten back by those of their European neighbours. Austrian and Moldavian advances encouraged an uprising in Târnovo in 1598, and the successful Austrian and Polish campaigns of the 1680s led to widespread revolt throughout northern Bulgaria. For the most part, however, life under Ottoman rule settled down to something approaching normality in the seventeenth and eighteenth centuries. Highland settlements such as Koprivshtitsa, Elena and Kotel were accorded privileges and allowed to accumulate wealth through trade, merchants sank their money into the renewal of churches, and the devshirme system gradually withered away. It was only with the disintegration of Ottoman provincial government in the late eighteenth century, and the emergence of the rapacious Turkish bandits known as the Kârdzhali , that the idea of Turkish rule as something fundamentally unjust and corrupt once again gripped the popular imagination. The partiality of the Ottoman legal system was one reason why many Bulgarians took to the forests to became haiduti , or outlaws.

Meanwhile, spiritual and artistic values predating the conquest were nurtured in the monasteries , which remained important repositories of Slav learning at a time when regular parish priests conducted services in Greek only. After the sixteenth century, the Bulgarian monasteries had restored contacts with Russia , a newly resurgent and rapidly expanding Orthodox power which came to be viewed as the great hope of the subject Christians of the Balkans.