This project focuses on the relationship between the World Trade Organization (WTO) and national courts, with a view to understanding the factors that can facilitate or hamper the rule of WTO law. In theory, if international law has domestic legal force and judiciaries are independent then we should expect to see both higher and lower national courts invalidate government economic policies that violate WTO legal rules, especially in the more advanced legal systems in the US, Europe, and Japan. In practice, however, we find that national courts even in these regions respond quite unevenly in striking down government policies when they go against WTO rules. What accounts for these uneven responses? This project tests three explanations-- legal precedence set at the domestic and international level, legal attitudes towards international law, and the domestic political context in which courts operate - across the three regions between 1947-2002. Overall, this analytical framework is vital to clarifying the conditions under which governments are more likely to abide by their treaty commitments and thereby promulgate the rule of WTO law in the global trading system.