This book brings to light the nature of the People of the Book and the People of a Dubious Book as understood in the Quran and Islamic Religious Tradition. The discussion is carried out both by analysing Islam as the only genuinely revealed religion as well as by addressing various Muslim scholars' attitudes and responses to the reality and nature of the People of the Book and the People of a Dubious Book apropos the Quran and the Islamic Religious Tradition. Evaluation of the nature of the People of a Dubious Book as exclusively developed by Abu al-Fath Muhammad Ábd al-Karim al-Shahrastani is also discussed.