This article examines the origins and contemporary materialisation of the provisions designating a definitional role to the Islamic religion and a supreme role to the Sharia within the constitutional frameworks of Arab nation states. In doing so, the article will examine the historical emergence of Islamic law as well as the historical formation of modern Arab nation states, prior to examining the continued modern manifestations of the Islamic religion and Islamic law within Arab constitutions and the relationship of such constitutional provisions to international law. This paper will show the way in which a decentralised Sharia adopted in autonomous territories was transformed into a centralised constitutional system through the emergence of a nation-state system in the Arab world. Within this context, and considering the role of European influence in the introduction of constitutional documents, the presence of Islamic religion and Sharia was retained within the centralised constitutional documents of the ‘new’ Arab nation states as a form of retaining Arab identity. In the context of common affronts to Islamic doctrines and the rapidly-changing landscape of the Arab world, the article also briefly addresses modern manifestations of Islamic law in constitutions and asserts that such constitutions do not affront nor contradict the role of international law within Arab states. Accordingly, this article will (1) firstly, examine the historical background of the emergence of Islam and Arab State formation, exploring the historical and theoretical bases of Islam in Arab constitutions as being inextricably linked to Arab identity; (2) secondly, address the way in which the Islamic religion and Islamic law are embodied in the modern constitutions of Arab states; and, (3) thirdly, inquire as to the relationship between such constitutional provisions and the role of international law within the constitutional legal systems of Arab states.