The European Union (EU) and United States (US) are the world's two largest and most influential legal jurisdictions for corporate mergers and acquisitions (M&A). The pressures of international economic competition have lead to a flurry of M&A activity in these locales in the post-Cold War period. Given the economic impact and, in many cases, political sensitivity of some M&As, it has become critical that transatlantic regulators reach similar decisions with regard to M&A approval, denial, or modification. Incongruent decisions lead to uncertainty in the marketplace, and the possible loss of global economic competitiveness and respect for regulatory processes and outcomes. In this paper, we explore the efforts made by the US and EU over the past two decades to enhance cooperation in merger policies and processes. We argue that, despite a couple of high-profile cases to the contrary, the US and EU have made great strides in reducing uncertainty in the M&A regulatory process by institutionalizing a series of formal agreements and working groups that have served to provide the foundation for a transatlantic merger environment that may serve as a model for cross-border regulatory cooperation in the twenty-first century.