The federal state structure adopted by Iraq in the post-2003 period in many ways represents a dramatic break with past traditions of government, both nationally and regionally speaking. Since Iraq formally came into existence as a monarchy in 1921, most of the country has been ruled as a centralised state, with Kurdistan as the sole area considered eligible for any special administrative status (which it enjoyed on paper since 1974 and in a more tangible, if unrecognised way between 1991 and 2003). As for the Gulf region more broadly speaking, with the exception of the special case of the United Arab Emirates, centralist state models have been the norm. This pattern can be seen both in Iran and Saudi Arabia, both of which are big countries with complex ethno-religious make-ups where external observers often have hinted about federalism as an alternative model of government, but where the reluctance to decentralise has so far been widespread. The major shift in Iraq's state model after 2003 concerns the possibility for implementing federalism in other areas beyond Kurdistan. Kurdish regional autonomy was recognised both in the Transitional Administrative Law (TAL) in 2004 and in the new constitution adopted in October 2005; additionally the possibility for creating new federal entities was enabled with a three-governorate size-limit in the TAL and without limitations in the constitution. Importantly, the constitution also establishes the principle of residual powers for all provincial units, whether they are governorates or enjoy federal status. The resultant patchwork is a federation where the theoretical powers of the central government are minimal, but where the dominant powers in Baghdad have nonetheless repeatedly made determined efforts to assert their authority beyond the constitutional remit and more in line with traditional Iraqi models of centralised government. This paper looks at the history of the institution charged with policing this complex situation: The federal supreme court. Through an investigation of 63 constitutional interpretations and 92 decisions in matters concerning the relationship between federal and provincial authorities in the period 2005-2009, the study outlines how the federal supreme court has navigated in a situation where the legal framework is ambiguous and the political pressures from both domestic and external players are considerable.