This chapter looks at the emergence of a politically and socially salient sense of Sunni sectarian identity in Iraq and beyond. To understand this phenomenon, one first has to understand sectarian relations before 2003 and by extension the implications of 2003 for Sunni and Shi‘a identity formation in Iraq and sectarian relations in the region generally. At its heart, the emergent and still evolving sense of Iraqi Sunni identity has been primarily shaped by two historic ruptures: regime change in 2003 and the ISIS takeover and subsequent war in 2014–2017. This chapter will primarily concentrate on the years 2003 to 2014: the consequences of regime change on sectarian relations, the Sunni reaction to the empowerment of a Shi‘a-centric political order, the inner paradoxes that marked Sunni-identity formation up to 2014, and the transnational impact that Iraq had Sunni identity formation. The post-2014 years have seen a marked shift in these processes. What distinguishes sectarian dynamics in pre- and post-2014 Iraq is the stabilisation of the post-2003 order, the normalisation and reintegration of Iraq into regional politics, the intra-Sunni divisiveness of the ISIS phenomenon and the victory of the state and its allies in the war that followed the ISIS surge in 2014.