Keynes and Bown explain the outsized importance of “zeroing”—a technical, yet politically controversial method the United States uses to calculate antidumping tariffs. They speak to Thomas Prusa (Rutgers University) about zeroing’s contentious negotiating history, how it works in practice, who is in favor of it, and how much trade is affected by it. They also discuss how the dozens of WTO disputes the United States has lost over this issue set up the current showdown facing the WTO Appellate Body and the future of the trading system.