This thesis analyses the Ottoman frontier organization in the Balkans from the second half of the fifteenth century to the early sixteenth centuries. Based mainly on the archival documents, Ottoman chronicles, and the secondary sources this thesis first shows that the Ottomans already had an established and comprehensive frontier policy, long before the conquest of the Hungarian Kingdom and the subsequent establishment of a new serhad against the Habsburg Empire. Then, it gives specific attention to the participation of Christian military groups (Voynuks, Martoloses, and Vlachs) and local subjects in the Ottoman defense organization in exchange for the reduction or exemption from certain taxes. Also, it deals with the hierarchical organization in the fortresses, the composition of the garrison troops and their services. Lastly, it concentrates on the Ottoman financing methods for the garrison troops and tries to reveal the cost of the Ottoman network of fortresses.