Kurdish separatism and Islamic fundamentalism, which were allegedly backed by Iran throughout the 1990s, were the two main factors which brought about the deterioration in bilateral relations. This article mainly focuses on the reasons for the great shift in current relations between Turkey and Iran. As the article shows, with the l1 September terrorist attack, the changing security perceptions of Iran stemming from American threats concerning Tehran’s building of nuclear weapons and sponsoring terrorism, pushed Tehran to develop better ties with Turkey. Similarly, Ankara wanted to strengthen its ties with the Iranian administration at a time when the PKK wished to be recognised as a political organisation of Kurds living in Turkey. Most important of all, the common objection of both countries, to the foundation of a Kurdish state in northern Iraq, has cemented relations. The study also seeks to analyse the current relationship between Iran and the United States in respect to understanding its impact on Turkey’s policies toward Iran