The Turkish power system suffers from frequency oscillations with 20 - 30 seconds period. This thesis focuses on solving the frequency control problem within the Turkish power system. Design criteria and requirements related to primary and secondary control are elaborated in order to establish the frequency stability of the isolated Turkish power system and to fulfil the requirements of the extended system after the interconnection of Turkey with the European system. On 18 September 2010 the Turkish power system was synchronized with the interconnected power systems of Continental Europe.