The ratification process for international treaties has become increasingly politicized in many democratic states. While scholars have devoted attention to the negotiation of international agreements, few have studied ratification struggles that define the ultimate success or failure of international commitments. Fewer still have examined the dynamics of this process in comparative perspective. In this article, I address this gap in the literature by exploring the politics of contemporary international treaty ratification processes in Canada and the United States. Drawing on two-level game theory, I posit that the likelihood of ratification success in these two different systems is often a function of similar dynamics in elite strategies for treaty ratification. Democratic leaders who sign international agreements must consider a range of factors, from the characteristics of the treaty itself to legislative pressures, interest groups, and public opinion in both parliamentary democracies and presidential systems. A structured, focused comparison of Canadian and U.S. case studies shows that the likelihood of successful treaty ratification depends primarily upon executive strategies within certain scope conditions. Given the challenges of minority government in Canada and deep political divisions in the U.S., this study also directs attention to the importance of coalition-building to ratify international agreements. Recent political developments in Canada and the United States suggest a trend toward politicization of international treaty ratification processes. In the United States alone, there have been more than five hundred instances of presidential endorsement that did not lead to congressional ratification. (2) Canadian Prime Minister Brian Mulroney was nearly defeated in a federal election in 1988 when he linked his political fate to the Canada-U.S. Free Trade Agreement (CUFTA), and President Bill Clinton won a narrow victory for North American Free Trade Agreement (NAFTA) ratification in 1993. The Kyoto Protocol prompted serious resistance from provincial leaders in Canada, and President Bush actually withdrew U.S. support for the treaty soon after taking office. Recent struggles over treaties offer important lessons about the relationship between executive leadership and international cooperation in many democratic systems. The outcomes of contested national elections in both countries in 2004 also raised the stakes in building political coalitions for controversial treaties. Minority government in Canada and deep political divisions in the United States mean that executives bear an even heavier share of responsibility in debates about treaties, international commitments, and sovereignty. Scholars have devoted a great deal of attention to the negotiation of international agreements, but few have focused on ratification struggles that truly define the success or failure of international commitments. (3) Fewer still have studied the dynamics of ratification struggles in comparative perspective. Yet breakdowns, and near-breakdowns, of international cooperation are surprisingly common in the ratification phase. This study investigates the role that executive strategies play in four case studies of U.S. and Canadian struggles over international cooperation. Research questions include: What are the legal and political requirements for ratification of an international agreement across democratic systems? How similar or different are ratification processes? What conditions influence the likelihood of ratification success? What conditions lead to failure? And, why would treaty ratification processes ever fail if the chief negotiators are fully aware of domestic political constraints? This study employs the comparative case study method for the purpose of exploring four episodes of treaty ratification struggles: 1. United States' ratification of NAFTA (1991-1993); 2. Canadian ratification of CUFTA and NAFTA (1988-1993); 3. …