This chapter discusses the Court’s 1978 judgment, Simmenthal, where the Court declared that all national courts – including ‘lower’ national courts – were under an obligation to apply European law in place of contrary national legal obligations, even if national constitutional rules restricted such powers to the national constitutional court. This judgment is often understood as an important one in the ‘politics of judges’ within the European legal order, reflecting the Court of Justice’s efforts to develop more active cooperation with ‘lower’ national courts than with national constitutional courts. This chapter demonstrates that the logic of Simmenthal is also derived from the use of national courts to enforce treaty obligations as a substitute for inter-state retaliation, as demonstrated by similar aspects of the enforcement provisions of the Side Agreements of the North American Free Trade Agreement (NAFTA).