This work elucidates Fakhr al-Din al-Razi's methodology in interpreting the Qur'an as expressed in his magnum opus known as Mafatih al-Ghayb or al-Tafsir al-Kabir. His rational approach to the interpretation of the Qur'an can be regarded as a consequence of his enthusiasm for the philosophical tradition. Basing himself on the assumption that the main function of the Qur'an is to give human beings guidance, Razi holds the view that everything in it has to make sense.