The topic of this chapter revolves around the internal and external determinants of Saudi-Iranian relations for the period from 2001 to 2016, and this chapter aims to interpret and analyze relations between countries in order to determine the extent of the continuity of relations and predict the behavior of countries. The study in this chapter concluded:
1- Explaining the stages of hardening and then détente in relations, according to each stage, its leaders, their personal characteristics and their actions.
2- The extent of the influence of geographical factors, human resources, national personality and the political development of countries.
3- The political environment in the countries is closed and the decision is for the guide, as he is the highest authority according to the constitution (Wilayat al-Faqih).
4- Likewise, the king, his deputy, the decisions, and the matter is a consultation in the royal family, who number 7,000 princes, and are involved in all fields.
5- With the emergence of oil, agreements were concluded with the United States, then crises occurred in the region and foreign forces were called in, then the events of September 11, 2001, then the war on terror, the occupation of Afghanistan and Iraq, and other repercussions.