The relationship between EU and U.S. antitrust regulators is widely considered to be a model of successful transgovernmental cooperation. With foundations developed primarily in the 1990s during the George H.W. Bush and Bill Clinton administrations, this relationship remained strong through the George W. Bush administration. Notwithstanding high profile transatlantic antitrust disputes in the Boeing/McDonnell Douglas and General Electric/Honeywell merger cases, cooperation generally predominated over conflict during this period. But at the time of the transition from the Bush administration to the Barack Obama administration in 2009, there were reasons to expect change in EU-U.S. antitrust relations. Some observers predicted that U.S. antitrust enforcement under Obama would be more vigorous than under Bush. Others expected Obama to place more emphasis on international cooperation than his predecessor, but with a focus on Asia more than Europe. In this chapter, we argue that notwithstanding these developments, there has been more continuity than change in EU-U.S. antitrust relations between the Bush and Obama administrations. While there continue to be occasional disagreements regarding both general approaches and specific cases, cooperation still predominates over conflict. And while antitrust regulators in both the European Union and the United States have had to adapt to a changing global environment, their intensified focus on the rest of the world does not appear to be undermining the bilateral EU-U.S. relationship.