This chapter looks at the thinking and practice of international relations and world order in the Islamic world. It opens by setting Islam's complex geopolitical context. In terms of thinking it covers the umma, the realms of al-Harb, al-Islam, and al-Ahd, jihad, the work of Ibn Khaldun, and Ijtihad. In terms of practice it covers the relationship between the umma and the Islamic state, the division of Islam into rival empires, and the rivalry between Sunnis and Shias within Islam. A key theme is the contradictions between thinking and practice.