Recent decades have witnessed a surge of trade in intermediate goods and a proliferation of free trade agreements (FTAs). FTAs use rules of origin (RoO) to distinguish goods originating from member countries from those originating from third countries. We focus on the North American Free Trade Agreement (NAFTA), the world’s largest FTA, and construct a unique dataset that allows us to map the input-output linkages in its RoO. Exploiting cross-product and cross-country variation in treatment over time, we show that NAFTA RoO led to a sizable reduction in imports of intermediate goods from third countries relative to NAFTA partners. (JEL F13, F15, F23, L14, O19)