The Tuna-Dolphin disputes between the United States and Mexico have spanned almost three decades. They have shed light on the “PPM debate”, i.e. whether trade restrictions based
on differences in process and production methods (PPMs) are justifiable under international trade rules. While a very strict approach against the use of PPM measures prevailed at the end of the GATT era, it has significantly evolved during the first two decades of the WTO. The Dispute Settlement Body eventually upheld a PPM “dolphin-safe” measure at the end of a particularly long judicial saga. The different Tuna-Dolphin reports show how environmental interests have gradually been integrated in WTO law and have influenced the interpretation of some of the core provisions of the GATT and the TBT Agreement (nondiscrimination obligations, general exceptions). These remarkable evolutions may be viewed as reflections of the objective of sustainable development mentioned in the WTO Agreement and as consequences of the judicialization of the multilateral trading system, which has allowed more legally sophisticated analyses based on the rule of law. They also illustrate efforts to foster the external legitimacy of the WTO, through greater sensitivity towards non-trade values. At the same time, the Tuna-Dolphin case law has become particularly complex, focusing on very fine technical details specific to the dispute, which has led to the risk of “never-ending story”. In this context, the search for legal security, coherence and efficient settlement of disputes may be the next challenge for WTO adjudicating bodies. At the same time, the use of PPM measures remains delicate and requires the assessment and balance of a variety of interests, including the specific interests of developing countries.