Introduction The surge of regionalism in recent years would seem almost by definition a development outside the sway of the United States, the global hegemon. Regionalism prioritizes the local; a hegemon exemplifies the global. Yet, at least since the end of the Second World War, the United States has been the most important actor in the global evolution of regional order1 and governance.2 Indeed, it is difficult to discuss almost any regional order without reference to the role of the United States. America is the world’s ‘omnipower’ in its involvement in almost all efforts at regionalism. The rise of new regional powers and the emergence of regional governance are also the product of many factors that have nothing to do with the United States. Yet, any effort to map and understand the trajectory of regional orders requires an understanding of the role of the United States therein. This relevance would seem to be obvious. What is surprising is how little it has been studied. The US role in international order and governance has been examined and theorized in many ways (Kindleberger 1973; Cox 1983; Wallerstein 1983; Keohane 1984; Gilpin 1987; Ikenberry 2002; Kupchan 2002; Nye 2002; Reus-Smit 2004; Jervis 2005; Lieber 2005; Walt 2005; Brooks and Wohlforth 2008). These studies, however, tend to ignore how international order relates to regional order and the role of the dominant global power in providing regional order. There has also, of course, been a surge of studies on regional powers and governance in the past 15 years (Fawcett and Hurrell 1995; Gamble and Payne 1996; Frankel et al. 1997; Mattli 1999; Fawcett 2004; de Lombaerde and Schulz 2009). Yet, that surge pays relatively little attention to the influence of the United States. This essay addresses that gap by attempting to answer a number of questions. Why have scholars not studied the topic more? How does the United States relate to regional governance? Why has the United States shown varying interest in different regions? How is the United States government organized to influence regional governance? How do US interests and actions interact with local concerns? How has the United States shaped the emergence of regional governance? What is likely to be the nature of the US relationship to regions in the future?