Writing on Saudi-Iranian relations is an uncertain endeavour, and any book on the topic runs the risk of being at least partially outdated even before it is published. Drawing on foreign policy theory, the chapters adduced several variables at different levels of analysis to explain the multi-faceted relations between the two countries. As the final manuscript of the book is being prepared for the publication (winter 2015), President Rouhani is more than halfway through his term. Since the end of the Iran–Iraq War in 1988 when this analysis began, the domestic, regional and international determinants of the two countries’ relations have gone a long way. The bilateral relations have since witnessed several ebbs and flows but are now as tenuous as they were in the years prior to 1989 when ties were broken off. At the regional level, two intractable conflicts rage on, one against Huthi rebels in Yemen and the other against Daesh. These conflicts have intensified the proxy war between the two countries. The human tragedy at the October 2015 Hajj stampede has been politicised as Iran and Saudi Arabia hurl accusations at each other. If Tehran’s relations with Bahrain are a barometer of the broader relationship between Iran and Saudi Arabia, then the recent mutual withdrawal of ambassadors in Tehran and Manama is a clear sign of a worsening of relations. It is reminiscent of the late 1980s when the two countries severed relations. In another surprising development, Ahmed Al-Mughassil, the key suspect and alleged mastermind of the Khobar bombing in 1996 who had gone missing for 19 years, was apprehended in Beirut and transferred to Saudi Arabia. Al-Mughassil’s capture would shed new light on the event, given that another main suspect of the attack, Imad Mughniyeh, is no longer alive.