Diffusion is the process by which economical, political, and cultural experiences are shared amongst countries. The international diffusion of planning ideas is defined as borrowing and imposition at national and local levels. In the case of Turkey, these experiences are viewed within the context of modernization and westernization. The most significant arena of this process took place in Istanbul. The process of adaptation began in the second half of the nineteenth century with the Tanzimat reforms and developed parallel to the degree of influence the United States and Europe had on the changes in the political regime and identity of the country in the wake of the two world wars. The financial support of the United States and World Bank investments sped up this process. A European Union harmonization process is now under way. The objective of this study is to relate the Turkish experience of international diffusion of planning ideas and evaluate the contribution of Istanbul’s spatial formation.