Saudi Arabia and Iran have established themselves as the two regional heavyweights in one of the world's most tumultuous but critically significant regions. The two countries compete on many fronts, including regional politics, oil prices, and for leadership of the Islamic world, a competition with undeniable repercussions for the Greater Middle East and for the world. Some observers have gone so far as to claim that virtually everything that happens in this area of the world can be viewed as part of the Saudi-Iranian power struggle. With increasing importance of the region as the dominant supplier of world energy and the birthplace of Islamic militant groups, the consequences of not understanding Saudi-Iranian rivalry in the region have never been more serious. A range of internal and external explanatory factors explains the ups and downs of Saudi-Iranian relations since the 1990s. This book captures this complexity by drawing on multicausal explanations through multiple levels of interdisciplinary analysis. This is the first book on the subject that is co-authored by one author from Saudi Arabia and one from Iran. This collaboration allowed the authors to make the best use of Persian and Arabic sources, generating a locally meaningful account of the two countries' relationship. As Iranian and Saudi nationals, they encountered less difficulty in gaining access to research participants, building rapport and conducting interviews with Iranian and Saudi scholars and informants.