Since 1979, the rivalry between Saudi Arabia and Iran – the two major powers in the Muslim world – has played a prominent role in shaping Middle Eastern politics. Political in nature yet couched in Islamic rhetoric, this rivalry reflects a desire to ensure regime security and legitimacy while also increasing influence across the Middle East. Since the 2003 Iraq War, the relationship has become increasingly vitriolic, resulting in the emergence of proxy conflicts in Iraq, Syria, Bahrain and Yemen. This book argues that to understand regional politics, comprehension of the rivalry between Riyadh and Tehran is essential. An electronic edition of this book is freely available under a Creative Commons (CC BY-NC-ND) licence.