Turkey’s role in the Iranian nuclear dossier is often portrayed as that of a ‘facilitator’ and ‘mediator’ in scholarly analyses. Due to its NATO membership and commitment to Western security cultures, Turkey was seen as a potential bridge-builder between the Islamic Republic of Iran and the ‘Western camp’ of negotiators. During prime minister Erdogan’s first legislature, however, Ankara’s and Washington’s foreign policy outlooks and strategic priorities started to diverge in the course of Turkey’s new regional engagement in what has been theorized as a ‘Middle-Easternization’ of Turkish foreign policy. It is Turkey’s location as a geostrategic hub in a politically instable region that informed Turkey’s ‘Zero problems with neighbors’ policy and foreign minister Davutoglu’s advocacy for a ‘Strategic Depth’ in Turkey’s foreign and regional policies. Ankara emphasizes its need to uphold good relations to its neighbors and Eurasian partners and publicly stresses its traditionally good bilateral relations with Teheran. This includes an unwillingness to go along with Western pressure on Iran, an insistence on the principle of non-interference, the Turkish repeated reiteration of Iran as a friend and of Iran’s right to use nuclear power for peaceful purposes. Against the background of the 2010 Brazil-Turkey-Iran nuclear fuel swap deal, recent studies have brought the ‘axis-shift’ discussion about a Turkish (security) political re-orientation away from the West and more towards regional engagement back to the fore and have emphasized a distinctive Turkish diplomacy with Iran that does not necessarily converge with ‘Western’ diplomatic preferences. However, Turkish-Iranian relations are undergoing a deterioration in the wake of the Syrian civil war at the time of writing, with both sides supporting diametrically opposite causes and factions. Turkish-Iranian fundamentally differing conceptions of regional order will also impact upon Turkey’s leverage power to defuse the Iranian nuclear crisis. Few analyses on this nexus have been produced so far. Process-tracing Turkey’s foreign policy in the Iranian nuclear dossier in the timeframe 2002-2012, this paper will thus add a timely contribution to our understanding of a multifaceted and nuanced Turkish foreign policy toward Iran that can be a critical complement to (or surrogate for) ‘Western’ diplomatic initiatives. The research method encompasses discourse and content analysis of policy documents (primary sources, e.g. declassified documents and press releases), as well as policy briefs and the scholarly literature, supplemented by semi-structured elite interviews with experts and decision-makers.