The United States and the European Union include several environmental clauses in their respective preferential trade agreements (PTAs). Building on an exhaustive and fine-grained dataset of PTAs’ environmental clauses, this article makes two contributions. First, it shows that the United States and the European Union have initially favored different approaches to environmental protection in their PTAs. The United States’ concerns over regulatory sovereignty and level playing field have led to a legalistic and adversarial approach, while the European Union's concerns for policy coherence have led to a more procedural and cooperative approach. Second, this article provides evidence that European and American trade negotiators have gradually converged on a shared set of environmental norms. Although the United States and the European Union initially pursued different objectives, they learned from each other and drew similar lessons. As a result, recent American agreements have become more European-like, and European agreements have become more Americanized. This article concludes that U.S. and E.U. approaches, far from being incompatible, can usefully be combined and reinforce each other.