As the urgency of climate change, biodiversity loss, severe poverty, and other global environmental and development challenges continues to grow, concerted international action to address them is becoming even harder. National efforts are thus more important than ever. An important example is the United Kingdom and the United States, which have stronger ties with each other than almost any other county — the so-called “special relationship.” They share a common language and history, and have similar legal systems and culture. The United States and the United Kingdom also aspire to international leadership, and often play that role. Accelerating the transition to sustainability requires six elements at the national level. These are a national strategy, legal integration mechanisms, governmental implementing or coordinating bodies, monitoring and review mechanisms, leadership, and a bottom-up sustainability movement. This article, coauthored with Professor Andrea Ross of the University of Dundee Law School in Dundee, Scotland, describes and compares key U.S. and U.K. actions on these elements, and suggests what each could learn from the other.