The tourism sector enables countries to reduce unemployment levels and attract foreign direct investment (FDI) which increase public welfare and economic activity. In this respect, it has a critical importance for specifically developing countries. In this article, the importance of tourism for developing countries will be mentioned and numerical data related to the sector will be presented. Among the developing countries, the example of Turkey, where tourism is of great importance, was chosen. The number of tourists, the share of tourism income in GDP, the share of the tourism sector in FDI and the employment opportunities provided by the tourism sector have been examined through the example of, Istanbul, which has developed in the tourism sector since the 1980s. Based on the mentioned criteria, the importance of the tourism sector for Turkish economy has been tried to be revealed.