This thesis explores Shi’a-Sunni relations in Gulf politics during a period of regional upheaval, starting with the 2003 invasion of Iraq through the Arab revolts of early 2011. It seeks to understand the conditions under which sectarian distinctions become a prominent feature of the Gulf political landscape, focusing on the three Gulf countries that have been affected most by sectarian tensions: Bahrain, Saudi Arabia, and Kuwait. The study analyzes the contagion effect of the civil war in Iraq, the 2006 war in Lebanon, and the Arab Spring on local sectarian dynamics in the three states. Specifically, it explores the role of domestic institutions—parliaments and other quasi-democratic structures, the media, and clerical establishments—in tempering or exacerbating sectarianism. It finds that the maturity and strength of participatory institutions in each state played a determinant role in the level of sectarianism resulting from dramatic shifts in the regional environment since the 2003 invasion of Iraq. I conclude, therefore, that the real roots of the so-called “rise of the Shi’a” phenomena lie in the domestic political context of each state, rather than in the regional policies of Iran or the contagion effect of events in Iraq or Lebanon. Although the Gulf Shi’a took a degree of inspiration from the actions of their co-religionists in Iraq, Iran and Lebanon, they ultimately strove for greater rights in a non-sectarian, nationalist framework. The rise of sectarianism in the Gulf has been largely the product of excessive alarm by entrenched Sunni elites or the result of calculated attempts by regimes to discredit Shi’a political actors by portraying them as proxies for Iran, Iraq, or the Lebanese Hizballah. What is qualitatively different about the post-2003 period is not the level of mobilization by the Shi’a, but rather the intensity of threat perception by Gulf regimes and Sunni Islamists.