Although a centralist education system is in place in Turkey, studies show that while implementing the curriculum developed by the Ministry of Education, teachers make changes based on their own preferences or depending on students. Curriculum fidelity can be defined as the degree to which teachers or stakeholders abide by a curriculum's original design when implementing it. Even though no clear position has been determined as to whether teachers' abiding strictly by the designed curriculum is beneficial or not, it is argued in the related literature that by determining fidelity of implementation, it is possible to explain the reasons for success or failure of curriculum innovations, and to specify the changes in the curriculum and their outcomes. In this study, the concept of curriculum fidelity is introduced through a review of the literature, then its historical background, importance, and methods of measurement are explored. Factors affecting curriculum fidelity and related research in the Turkish context are presented, and prominent features of curriculum changes reflected on the practice of education are studied. It is concluded from the study that the factors affecting curriculum fidelity in Turkey are teacher characteristics, curriculum properties, teacher training, institutional features, regional, social, economic, and cultural characteristics, a centralist education system, high-stakes tests, and student characteristics. Because of the understanding of viewing teachers as technicians responsible for implementing a curriculum designed by experts and directors, it cannot be possible to have expert staff that can adapt the curriculum to the conditions of their region, school, or class. This vicious circle drives teachers to ambiguity in planning and implementation; teachers having difficulties abiding by the curriculum under the conditions of the region, school, and class carry out curriculum implementations different in theory and in practice. Suggestions for practice and future research are also included in this study.