The purpose of this thesis is to provide a comprehensive account and detailed analysis of the forces that led to the emergence and consolidation of the Syrian-Iranian alliance during a turbulent decade in the modern history of the Middle East. The alliance between the two states, which has now lasted over twenty years, has proved to be an enduring feature of the political landscape of this troubled region. Moreover, since its inception, it has had a significant impact in terms of moulding events and bringing about major changes in the contemporary Middle East. The thesis sets out to demonstrate that, contrary to prevailing views (due in large part to the authoritarian nature of the Syrian and Iranian regimes and their unpopularity in the West), the alliance between them has been essentially defensive in nature. It emerged in response to acts of aggression orchestrated by Iraq (1980) and Israel (1982), in both cases with the tacit support and prior knowledge of the United States. As a result of the research undertaken for this thesis, three distinct phases in the evolution and institutionalization of the Damascus-Tehran axis can be discerned. One chapter is devoted to each of these phases, constituting the three core sections of the thesis. A brief introduction sets out to provide a conceptual framework for understanding the genesis and evolution of the Syrian-lranian nexus. The first core chapter, covering the emergence of the alliance between 1979 and 1982, demonstrates that, while the initial impetus for the birth of the relationship came from the overthrow of Iran's conservative, pro-Western monarchy in 1979, the Iraqi invasion of Iran in September 1980 served as a major catalyst in bringing Syria and Iran closer together, with Syria providing valuable diplomatic and military assistance to help Iran stave off defeat. The second core chapter covers the period between 1982 and 1985, when Israel launched an invasion of Lebanon and challenged Syria in its backyard. Here, Iran lent its support to Syria to drive out Israeli and Western forces during the period 1983-1985. The third core chapter deals with a critical, and perhaps the most problematic, phase in the development of the alliance. By the mid-1980's, both parties had developed conflicting agendas, contributing to tensions between them. However, continued consultations between the two allies, and their ability to prioritize their respective interests and redefine the parameters for cooperation, led by the late 1980s to the maturation and consolidation of their relationship. Finally, the conclusion looks at the reasons why the alliance lasted beyond the 1980's