Istanbul is not only a culture and civilization center but also a cosmopolitan world city which hosts different religions and ethnical backgrounds. On that account, Istanbul has been a focal point for different missionary societies. First missionaries to visit Istanbul during the Ottoman period were Catholics mainly from Italy and France. Protestant missionaries from the United States have followed Catholics in the 19th century. By aiming to convert people into their own belief, these missionary organizations have initially established new cultural and educational institutions. Still being active in today's Istanbul, these institutions educated numerous students during the Ottoman and Republican period. Besides, Turkey is one of the main missionary destinations during 2000's in terms of global missionary activities conducted by different societies. This study aims to bring an understanding on the arrival purpose of the missionaries, the established mission schools and cultural foundations by examining case events. In addition, the effect of these activities on Turkish educational and cultural life will be discussed.