This paper examines the main drivers underlying relations between the Islamic Republic of Iran and the Saudi monarchy from 1979 to the present day. Through observations, analysis, and comments on the events punctuating their dealings with each other, the author sheds light on the complexity of a relationship played out in the ever-present shadow of the United States. He examines historical, religious, ethnic, political, theoretical, ideological, military, diplomatic and empirical events to demonstrate that through successive phases of friendship and hostility, the relationship between these two contenders for hegemony in the Gulf has more often than not been one of mistrust.