This thesis introduces a history of evangelical American Protestant missionary experience in Ottoman Istanbul during the nineteenth century. It argues that the New England Puritan heritage from the eighteenth century determined the scope and objectives of American missionaries in the Ottoman Empire although the missionaries sometimes disagreed with the missionary plans set by the ABCFM Prudential Committee in Boston. Contrary to the expectations of the American Board, the missionaries directed their full force to teaching often more than preaching once they landed in Istanbul. They believed that the natives of Istanbul needed education, attributing their backwardness and lack of faith to iliteracy. At the turn of the twentieth century, their institutions became prototypical and the later missionaries in the Middle East modeled their missions on those missionary establishments in late nineteenth-cenury Istanbul. Overall, the thesis, with its emphasis on the continuities and changes in evangelical American missionary mindset, the successes and failures of the missionary activities in the Ottoman capital, and the American missionary experience and life with the Ottomans, revises and provides fresh insights into American religious attitudes, relations between Ottomans and Americans, and the American "Errand into the East."