“Reason” and “Rationality” have been the most controversial subjects in human thinking. Question of reason is faced not only with questions about the capacity of reason to discover truth, the possibility of choice, and the decisive role of reason in epistemology, but also it deals with questions about thought, freedom, and the nature of thought. Reason is a common point among all human beings; therefore, there is no difference between people in the amount of intellect, but the differences are due to the dominant epistemological paradigm in each period and the impact of historical, social and cultural conditions on the interpreting of that paradigm of intellect. In the last few centuries, the concept of reason and rationality has encountered major challenges. Western epistemological approaches such as post structuralism and methodological approaches such as genealogy, seek to find gaps of this concept in the historical process. On the other hand, the concept of reason in Islamic thought and its relationship with religion has always been controversial. Some contemporary Muslim thinkers, by giving originality to reason and respecting Western modernity, have a critical approach to traditional society and the way to achieve an ideal society with new outlook such as pluralism, critical religious rationality and democracy in a religious society based on rationality. Some other Muslim thinkers, by proposing views such as the theory of rationality and spirituality, go beyond the modernist approach to religion, seeking a way to avoid religious intellectual contradictions. This article tries to examine both Western and Islamic perspectives on reason and rationality.