The case United States — Measures Concerning the Importation and Marketing and Sale of Tuna and Tuna Products concerns whether United States “dolphin-safe” labeling requirements comply with the Agreement on Technical Barriers to Trade (TBT Agreement) of the World Trade Organization (WTO). This paper analyzes the WTO Appellate Body decision and its systemic importance for the interpretation of the TBT Agreement’s substantive obligations; the types of labeling that fall within the scope of the Agreement; the legitimacy of labeling based on foreign process and production methods (PPMs); and the relation of other international law to WTO law.